Car Ramp Angle & Length Calculator

A car ramp calculator turns a ramp’s rise and length into its angle and percent slope. For example, a 6-inch rise over 36 inches of ramp surface is about 9.6°, or a 16.9% slope. If you add your car’s approach angle, it also shows the ramp length a low car needs.

1. Pick your units: inches or centimetres. All lengths use the same unit.
2. Choose which length you have. The default is the length along the ramp surface (L), measured with a tape laid on the slope. The alternative is the horizontal run (D): the floor distance from the ramp toe to the point directly below the top. Many ramp listings do not say which one they mean, so check the maker’s definition and do not assume.
3. Enter the rise (h): the vertical height from the floor to the top of the ramp, where the tyre rests.
4. Enter the length or run. The results update as you type.
5. Optional: enter your car’s approach angle from the owner’s manual or the maker’s spec sheet. If no figure is listed, enter the front clearance (c) and overhang distance (o) instead. A directly entered angle takes precedence over c and o.

The tool shows the ramp angle in degrees, the percent slope and the other length. When an approach angle is available, it also shows whether the ramp is steeper than that angle, the minimum ramp length, its floor footprint and any extra length needed. A scaled triangle diagram under the results labels the rise h, the surface length L, the horizontal run D and the angle θ. When an approach angle is set, the diagram adds it as a dashed line from the ramp toe.

A ramp forms a right triangle. The rise h is the vertical side, the horizontal run D is the floor side, and the length along the surface L is the sloping side. The ramp angle θ sits at the toe.

• Length along the surface (L) known: θ = asin(h / L), and D = √(L² − h²).
• Horizontal run (D) known: θ = atan(h / D), and L = √(h² + D²).
• Percent slope (both modes): slope % = h / D × 100.
• Approach angle from measurements: α = atan(c / o), where c is the height of the lowest front point and o is its horizontal distance from the front tyre’s contact point.
• Minimum ramp length for the car: L_min = h / sin(α), with floor footprint D_min = h / tan(α). The extra length needed is L_min − L, shown only when it is positive.

Both modes give the same angle and slope when they describe the same triangle. The test cases below are pure arithmetic, not data for any real car or ramp. You can check them with any scientific calculator.

Slope versus angle. Percent slope is the rise divided by the horizontal run, times 100. It equals 100 × tan(θ), so a 45° ramp is a 100% slope, not 50%. Dividing the rise by the length along the surface gives the sine of the angle instead. That is why a ramp’s rise and its surface length do not give the percent slope directly. The tool first works out the horizontal run, then calculates the slope.

Ramp length for a low car. A car’s approach angle is the steepest incline its front end can meet without touching. If the ramp angle is steeper than that, the front lowest point may touch the ramp at its base. Long car ramps for low cars work by spreading the same rise over a longer surface, which lowers the angle. The calculator gives the minimum surface length, L_min = h / sin(α), and shows how much longer than your current ramp it is.

In test case 4, an approach angle of 9.46° and a 6-unit rise need about 36.50 units of ramp surface. A 36-unit ramp would be about 0.50 short. Treat this as an estimate and confirm it against the ramp maker’s stated maximum angle.

This tool checks base-of-ramp contact only, using straight-line geometry. It does not check the top transition or breakover, underside clearance along the car, ramp weight capacity, stability, or floor surface and grip. It does not judge whether any ramp or setup is suitable for your car. The ramp maker’s maximum angle, rating and manual govern.

Never work under a vehicle supported only by a jack. Follow the maker’s rating and manual and ASME PASE, the Safety Standard for Portable Automotive Service Equipment. Its published scope covers jacks, stands, ramps and related equipment.

An NHTSA/NCSA Research Note from September 1998, based on CPSC NEISS data for 1994–95 (old data), states: “Approximately three-fourths (74%) of the persons injured in motor vehicle jack failures were injured as a result of being struck by the vehicle as it fell from the jack.”

NIOSH FACE Report 99CA006 (1999) involves a transit bus on shop-made stands, not a car. It reports: “A 48-year old male mechanic (decedent) died when he was crushed by a bus that fell off jack stands.” It recommends that employers “ensure employees use only tools and equipment that have been tested, certified and rated.”

No official US fatality count exists for jacks or jack stands in these sources.

All results are computed in your browser from your inputs. No product data, prices or external datasets are used. Lengths are converted internally to millimetres (1 in = 25.4 mm exactly) and shown in your chosen unit. Rounding is applied once, for display only: angles to 0.1°, slope to 0.1% and lengths to 0.1 unit. The diagram is drawn from the unrounded values. Input bounds (rise 0.1–60 in or 0.25–150 cm, length up to 240 in or 600 cm) exist only to catch typos. They are not safety limits.

• Wikipedia, “Grade (slope)”: percent slope = 100 × rise/run = 100 × tan(angle); rise over slope length gives the sine.
• Wikipedia, “Inch”: 1 in = 25.4 mm exactly.
• NHTSA/NCSA Research Note (1998), Injuries Associated With Hazards Involving Motor Vehicle “Jack Failures”: CPSC NEISS data, 1994–95.
• NIOSH FACE Report 99CA006: mechanic crushed by a bus that fell off jack stands (1999).
• ASME PASE, Safety Standard for Portable Automotive Service Equipment: cited by name and scope.

Last updated: October 2026

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