Driveway Slope Calculator

How to use the driveway slope calculator

Four tabs. Pick the one that matches what you already have.

Rise & Run. The height the driveway climbs and the flat distance it covers. This is the one most people want. Measure the run flat along the ground, not along the surface of the drive.

Two Elevations. A start height, an end height and the distance between them. Use this when you have survey figures, a site plan, or a phone app that gives you elevation at each end.

Percent Grade. You already know the grade and want it back as an angle and a ratio, or you want the rise a given run produces. Add the run and it fills in the height.

Grade & Rise. The planning tab, and the one to use before anything is poured. Give it the grade you are limited to and the height you have to climb, and it returns the length that takes. A 4 ft 6 in climb at a 12% cap needs 37.5 ft of run, and if you do not have 37.5 ft the answer is that the driveway does not fit, which is better to know now.

Under every tab sit five optional boxes, and they run the scrape check. Each one answers a different question, and none of them stands in for another. Leave them all blank and you still get every grade number.

• Ground clearance and wheelbase, both in inches, both off the spec sheet. Together they check the crest: the break at the garage on a driveway that climbs, or the break at the street on one that drops to a basement garage.
• Vertical curve length in feet. This is the full length between the two constant-grade sections, not the part that looks curved. If the two grades meet at a corner, which is what most driveways do, leave it at zero.
• Approach angle in degrees, for driving in nose first. This checks the sag at the other end, where the nose drops rather than the belly lifts. Take it from the spec sheet: Ford publishes 23.3 degrees for a 2026 F-150 SuperCrew 4×2, Honda publishes 17.7 for a 2025 CR-V LX 2WD.
• Departure angle in degrees, for backing out. Reversing down the drive puts the rear overhang across the same sag, and it is a different number on the same car: 24.3 on that F-150, 21.3 on that CR-V. Ground clearance and wheelbase will not give you either of these. They have to come off the spec sheet.

One thing that trips people up before they even start. A driveway is rarely one grade. There is usually an apron at the street, a main run, and a flatter stretch at the garage. Measuring end to end averages all three and gives you a number that is comfortably wrong. Measure the steepest stretch on its own, because that is the one that governs.

What you get back

• The grade, four ways. Percent, angle in degrees, ratio written 1:n, and the decimal.
• The geometry. Rise, run and the slope length, which is the paving you buy rather than the ground it covers.
• A comparison box that places your grade in the spread of eight published US driveway limits, five of them municipal code and three agency design standards, all read in full.
• The crest check, when a ground clearance and a wheelbase are entered: the clearance the crest actually demands, how much you have, and the steepest sharp break that car can straddle.
• The sag checks, one for the nose when an approach angle is entered and one for the tail when a departure angle is entered: whether each clears the break at the other end, and by how much.

Read that box as a comparison, not as a compliance check, because that is all it can be. It sets your number against eight headline maximums, and a headline maximum is not the only rule those documents contain. Three of the eight hold the first stretch off the street to a tighter grade than the driveway as a whole:

• Mountain Village CO allows 8% overall and 5% for the first 20 feet from the edge of the public road.
• Bernards Township NJ allows 10% overall and 8% for the first eight feet from the curbline, with a transition curve required after it.
• Inver Grove Heights MN allows 27% from the property line to the garage and a quarter inch per foot, about 2.1%, across the boulevard from the top of the curb.

Three more come close without being the same thing. Los Angeles requires the approach to accommodate a 2.5% upward slope off the curb, which prescribes an apron rather than capping one. Burbank requires a grade transition at each end and attaches no number to it. Seattle’s 10% is a whole-driveway figure that applies when access is back-in only. A driveway can sit under every headline figure on this page and still fail at its own entrance.

There is no national limit, the eight run from 8% to 27%, and the only authority on your driveway is the office that permits your curb cut.

How precise the numbers are

Grade carries three decimals, the angle three, slope length four, and nothing rounds until it prints. The crest and sag checks print two decimals in inches and two in degrees, because a hundredth of an inch is already finer than a driveway gets poured to.

About units

Feet, inches, yards, metres, centimetres and millimetres. Rise and run only have to match each other, because grade is a ratio and the units cancel out of it.

The four scrape boxes are the exception, and they ignore the unit selector on purpose. Ground clearance and wheelbase are spec sheet numbers, given in inches. A vertical curve is something you pace out, so it takes feet. An approach angle is always degrees. Every unit is written into its label, because reading a wheelbase given in feet as inches would not fail, it would print a confident wrong answer.

One more habit worth breaking. Grade is a percent here because that is how roads, driveways and site plans are written. Ramps and accessibility work use a ratio instead, which is why the same slope reads as 8.33% on a driveway plan and 1:12 on a ramp drawing.

The driveway grade formula

Grade is rise divided by run, times a hundred. Everything else on the panel is that one division written a different way.

• grade = (rise ÷ run) × 100
• angle = arctan(rise ÷ run)
• ratio = 1 : (run ÷ rise)
• slope length = √(rise² + run²)

How to calculate driveway grade by hand

The garage floor sits 4 feet 6 inches above the gutter, and the drive covers 38 feet of flat ground between them.

1. Put both in one unit. 4 ft 6 in is 4.5 ft. The run is 38 ft.
2. Divide. 4.5 ÷ 38 = 0.11842.
3. Grade. 0.11842 × 100 = 11.84%.
4. Angle. arctan(0.11842) = 6.75°.
5. Ratio. 38 ÷ 4.5 = 8.44, so 1:8.4.
6. Slope length. √(4.5² + 38²) = 38.27 ft, so about 3 inches more paving than the run suggests.

Note the angle. A driveway most people would call steep is under 7 degrees. That gap between the percent and the degree is where most of the confusion on this subject lives.

Driveway grade in percent, degrees and a ratio

Three ways of writing the same measurement, and every trade picks a different one. Site plans and codes use percent. Machinery specs and vehicle data use degrees. Drainage and accessibility work uses a ratio.

Percent	Degrees	Ratio	Rise per 10 ft
1%	0.57°	1:100	1.2 in
2%	1.15°	1:50	2.4 in
5%	2.86°	1:20	6.0 in
8%	4.57°	1:12.5	9.6 in
10%	5.71°	1:10	12.0 in
12%	6.84°	1:8.3	14.4 in
15%	8.53°	1:6.7	18.0 in
20%	11.31°	1:5	24.0 in
25%	14.04°	1:4	30.0 in
30%	16.70°	1:3.3	36.0 in

Why a 15 percent driveway is not a 15 degree driveway

Percent and degrees are not two names for one number, and they do not track each other. 15% is 8.53 degrees. 15 degrees is 26.8%, which is nearly twice as steep and above every headline figure in the table further down this page except one.

They only meet at 45 degrees, which is 100%, because that is the one slope where the rise and the run are equal. Everywhere below that, the percent figure is the larger of the two, and the gap widens as the grade steepens.

This is not a pedantic point. It is a common error, it turned up in most of the driveway threads we read, and it runs both ways. Someone describes a 30 degree driveway that is really 30%, and gets advice for a slope nearly twice as steep as the one they have. Someone else reads a 17.1 degree breakover figure off a spec sheet, compares it to their 20% driveway, and concludes the car will ground out. It will not. A 20% break deflects by 11.31 degrees, not 20, and 11.31 is comfortably inside 17.1.

What the maximum driveway slope actually is

Search this and you will be told 15%, or 25%, with total confidence and no source attached. Both numbers trace back to nothing checkable. Here is what is actually true.

There is no national maximum driveway slope in the United States. The International Residential Code does not set one, and at section R105.2 it lists sidewalks and driveways among the work exempt from permit. Be careful how far you take that second point: R105.2 also says an exemption from permit does not authorise work that violates the code or any other law. It means the IRC is not the document that governs your driveway grade. It does not mean nothing does.

ICC does publish a driveway slope provision, but it is in a different book, the International Zoning Code at section 801.4.2, which few jurisdictions adopt. We have not put a number to that section here because its text sits behind a paywall and we have not read it.

The 10% that gets quoted as though it were code is International Fire Code appendix D103.2, which reads that fire apparatus access roads shall not exceed 10 percent in grade. Three things about it. It is an appendix, and IFC section 101.2.1 says appendix provisions do not apply unless a jurisdiction specifically adopts them. The section carries an exception allowing steeper grades where the fire code official approves. And jurisdictions rewrite the number when they do adopt it: Red Bluff, California, adopting the 2021 IFC, amended D103.2 to read 12 percent, with an exception to 15. It also governs an access road, which in most places is not the same thing as the driveway to a single house.

The limit that applies to you is local, and it is set by zoning, by the public works standard for your curb cut, or by your fire district.

What this means in one paragraph. Eight published US standards, five of them municipal code and three agency design standards, cap residential driveways somewhere between 8% and 27%. Half of them stop at 12% or lower. Three also hold the first stretch off the street to something tighter than the driveway as a whole. Nobody can tell you your number is allowed except the office that issues your curb cut permit, and what they will ask for is a profile of the whole driveway, not one grade. Here are the eight, read in full and linked so you can check them:

Jurisdiction	Max grade	Where it is written
Mountain Village, CO	8%	MVMC 17.6.6.B.4, and 5% for the first 20 ft off the road. Transitional sections reach 10% with Fire Marshal approval, or 12% where every home has sprinklers
Draper, UT	10%	City Code 9-27-160, 12% in the Hillside Sensitive Lands Overlay Zone
Bernards Township, NJ	10%	Code 21-38.1b, and 8% for the first eight feet from the curbline, with a transition curve required
Boulder County, CO	12%	Driveway Access for Emergency Vehicles, form W/04. 14% for up to 200 ft in the mountains, 16% for a single dwelling
Los Angeles, CA	20%	Bureau of Engineering Complete Street Design Manual E 535.3, written as should not exceed rather than shall
Seattle, WA	20%	Streets Illustrated 3.1, and 10% where the access is back-in only
Burbank, CA	20%	Municipal Code 10-1-1604, plus a required grade transition at each end
Inver Grove Heights, MN	27%	City Code 10-15-20(D), which also sets a 0.50% minimum

The range is 8% to 27%, and the eight do not sit evenly across it. Four stop at 12% or lower, three allow 20%, and one allows 27%. The 12% mark is worth noting on its own: it is what the Texas Department of Transportation suggests for private residential driveways in Roadway Design Manual section 16.3.1, alongside 8% for everything else and 6% or less inside the road right of way. TxDOT is a design manual rather than a code, and it says should, not shall.

One entry came out of this table on the way here, and it is worth saying why. Richland, Washington caps driveways at 10% in RMC 12.04.095, and that section is headed Width of driveways, Nonresidential and opens by defining everything other than a single residence driveway as nonresidential. Its 10% never applied to the driveways this page is about, and chapter 12.04 sets no grade limit for a single-residence driveway anywhere. It is the kind of figure that gets repeated for years because the number is real and the scope is never checked.

Two more numbers that leak into US search results and do not belong there. The 20% and 25% pair, and the 1:8 transition rule that travels with them, come from AS 2890.1, the Australian and New Zealand parking facilities standard. It has no force in the United States. And 13.3% appears constantly as a change of grade limit: that is PROWAG R304.5.2, which sits inside a section titled Curb Ramps and Blended Transitions, applies to pedestrian routes in the public right of way, and is written as an either/or with a transitional space. It has nothing to say about a car bottoming out.

At the shallow end there is a floor as well as a ceiling. Los Angeles designs driveways between 1% and 6% where the site allows it, Inver Grove Heights writes a hard 0.50% minimum into code, and Cincinnati’s driveway approach permit procedure calls 2%, a quarter inch per foot, the optimum slope at the sidewalk. Below about 1% you are relying on the surface being flatter than concrete is usually finished.

One caution on reading the calculator here. A grade is one number along one line, and the box can tell you that line has no fall. It cannot tell you the driveway does not drain, because a flat-looking drive with a proper cross slope or a crown sheds water sideways perfectly well. Nor can it tell you which way the fall goes: a driveway falling to the street is fine, and the same number falling toward a garage is a flood waiting for the right storm, and the difference is not the grade, it is whether the low end has a drain with somewhere to send the water.

Checked August 2026. Every figure above was read from the published text of the document it is attributed to, and each one is linked so you can check it yourself. Codes are amended, appendices are adopted selectively, and hillside and fire overlays routinely override the base number in both directions. Your permit office is the only authority on your driveway, and the drawing they will want is a profile, not a single grade.

Why a car scrapes on a driveway that passes the grade check

This is the question almost everyone is really asking, and the grade does not answer it. Cars do not scrape on the slope. They scrape at the two places where the slope stops.

Every driveway has a crest and a sag. Climb from the street to the garage and the street end is a sag and the garage end is a crest. Drop from the street to a basement garage and the two swap over. They deflect by exactly the same angle, and that angle is simply the slope angle the calculator already printed, because both breaks meet flat ground.

What they catch is different, and this is the part that gets missed:

• The crest catches the belly. The front wheels are on the flat, the rear wheels are still on the slope, and the lowest point between the axles has to pass over the corner. That is the ramp breakover angle, SAE J1100 code H147.
• The sag catches the nose. The wheels drop into the dip and the front overhang keeps going. That is the angle of approach, code H106, or the angle of departure, H107, when you back out. Overhang decides it, not wheelbase.

Fixing one does nothing for the other. Bolting a rubber ramp at the curb helps a sag and can make a crest worse. This is also why the fix that works is almost always length, not grade.

What a transition actually does

Round the corner off over a length and the ground under the car stops lifting so fast. For a vertical curve of length L with an algebraic grade change of A percent, and a wheelbase W, the crest rises above the line joining the two tyre contact patches by A × W² ÷ (800 × L), with W and L in feet and the answer in feet. L is the full length of that curve, measured from where the first constant grade ends to where the second one begins, and not just the stretch that looks rounded. Guessing it short is the same as guessing the driveway steeper than it is. The car clears when that is less than its ground clearance.

Look at what is not in that expression. Once the curve is longer than the wheelbase, A appears once and L appears once, underneath. Double the transition and you halve the clearance you need, whatever the grade is. That is the whole mechanism, and it is why a long driveway can be steeper than a short one and still work.

Worked, on a 2026 Ford F-150 SuperCrew 4×2: wheelbase 145.4 in, so 12.12 ft, ground clearance 8.2 in. At a sharp 20% break the crest lifts 7.27 in under the belly, which clears 8.2 in by less than an inch. Give that same break a 10 ft transition and it drops to 4.27 in. At 5 ft it is 5.77 in. Nothing about the driveway’s grade changed in any of those three.

This is what TxDOT is doing with two separate rules rather than one. Table 16-4 suggests a maximum change in grade of about 10% for private residential driveways and 8% for everything else, at the break between the road cross slope and the apron. Then separately, section 16.3.1 recommends a minimum K value of 4, where K is the curve length divided by the grade change, for driveways serving low ground clearance or long wheelbase vehicles. The first bounds how sharp the corner is allowed to be. The second bounds how quickly it turns. Quoting either one on its own misses the point of having both.

Two numbers people compare that are not comparable

Here is the mistake that costs money, and no driveway page anywhere makes it clear.

A grade change in percent is not an angle in degrees. A 20% break deflects by 11.31 degrees. Set that beside a published breakover angle of 17.1 degrees and the car clears with room. Set 20 beside 17.1 and it looks like a fail. Same driveway, same truck, opposite conclusion, and the only difference is that one comparison converted the units and the other did not. If you take one thing from this page, take that: convert the grade to degrees before you compare it to anything off a spec sheet.

And the clearance estimate is a floor, not the spec. This calculator works out the steepest break your car clears from ground clearance and wheelbase, because those are two numbers anyone can look up. The formula has to assume the lowest point on the car sits halfway between the axles. It usually does not. On that same F-150, 8.2 inches over a 145.4 inch wheelbase gives 12.87 degrees, while Ford’s own spec sheet gives a measured breakover of 17.1. The estimate is more than four degrees pessimistic, and it is pessimistic in a useful direction.

Do not read a pass as a guarantee, though, because the belly-point assumption is only one of the things this cannot see. Ride height drops with a loaded car, with worn tyres, with soft suspension, and with three passengers in the back. A real break is not the clean corner the geometry assumes: there is a gutter, a crown, and whatever tolerance the concrete crew worked to. And SAE measures to the actual lowest structure, which on your car might be an exhaust hanger, a splash tray or a hitch rather than the point the formula imagines. Treat a pass as encouraging, find the manufacturer’s published breakover and approach figures if the margin is thin, and leave yourself a degree or two either way.

Most sedan makers publish no breakover figure at all, which is exactly why this goes wrong so unpredictably in a car and so predictably in a truck.

The vehicles that decide for you

Your own car is not the only thing that has to get up the drive. Fire apparatus access is the one with a written number, at 10% in IFC appendix D103.2 where a jurisdiction adopts it. Mountain Village holds fire apparatus turnaround areas to 5 or 6 percent and allows 12 only where every home is sprinklered. Beyond that, there is no published US standard capping grade for garbage trucks, moving vans, propane deliveries or ready-mix. Every figure circulating for those is somebody’s recollection. Call the company and ask before you pour, because a concrete truck refusing the drive on the morning of the pour is a genuinely common way for this to go wrong, and by then the only fix is a pump.

5 reasons a driveway gradient comes out wrong

1. Measuring the run along the surface. Run is the flat distance, the shadow the driveway casts at noon. Pulling a tape up the slope gives you the slope length, which is always longer, and the grade you get back is always too shallow. A true 20% drive reads back as 19.6% if you measure the run up the surface.
2. Averaging the whole driveway. An apron, a main run and a flat pad at the garage measured end to end give one number that describes none of them. The steepest stretch is what scrapes, what ices, and what the permit office looks at.
3. Reading a percent as an angle. Covered above, and it is the most common of the five by a wide margin.
4. Measuring to the wrong end of the apron. The rise starts at the gutter flowline, not at the sidewalk or the property line, and the first few feet off the street are frequently held to a tighter grade than the rest. Bernards Township allows 10% overall and only 8% for the first eight feet.
5. Trusting a phone level held against the dashboard. Phone inclinometers read the phone, and a phone against a car reads the car’s suspension attitude, not the ground. Lay a four foot level on the surface and measure the gap at the low end instead. Divide the gap in inches by 48 and multiply by 100 for the grade.

Water is worth a note of its own. A driveway that falls toward the house needs somewhere for the water to go, and the grade alone does not decide whether it gets there. That is a question about the drain, not the drive, and a trench drain needs its own fall to work, typically a quarter inch per foot. A channel with no outfall fills up in the first real storm, which is the most common version of a flooded garage.

Frequently asked questions