Road grade (or gradient) is the ratio of vertical rise to horizontal run, expressed as a percentage: Grade (%) = (Vertical Rise / Horizontal Run) × 100. A 6% grade rises 6 units vertically for every 100 units of horizontal travel.

Does road grade use horizontal run or traveled slope distance?

Standard civil surveying and highway engineering (FHWA) define grade using horizontal map projection (run), not the inclined hypotenuse (slope distance). Slope distance is computed via the Pythagorean theorem: √(Rise² + Run²).

How do you convert grade percentage to degrees?

Slope angle θ in degrees is the arctangent of the decimal slope: θ = arctan(Grade / 100) × (180 / π). For example, a 10% grade is arctan(0.10) ≈ 5.71°.

How is slope ratio (1:n) defined?

A slope ratio of 1:n expresses 1 unit of vertical rise for every n units of horizontal run. For example, an 8.333% grade equals 1:12, and a 1% grade equals 1:100.

Does this calculator determine ADA compliance?

No. The U.S. Access Board specifies a maximum 1:20 running slope for accessible-route walking surfaces and 1:12 for ramps governed by section 405, but full compliance also depends on other requirements. Use the official standard and applicable local rules.

Road Grade Calculator

Calculate grade percent, angle, elevation change, slope length, and gradient ratio (1:n) with explicit input modes and signed uphill/downhill direction.

Slope Parameters

Select your known pair to calculate vertical grade, angle, ratio, and distance.

Calculation Mode

Linear Distance Units

Vertical Rise / Drop

units

Horizontal Run

units

Calculated Grade & Alignment

Enter your slope parameters and click Calculate.

Slope conversion examples

Specification / Context	Grade (%)	Angle (°)	Ratio (1:n)
1:100 Civil Grade Base	1.000%	0.573°	1 : 100
ADA Accessible Route Max (walking surface)	5.000%	2.862°	1 : 20
ADA Section 405 Ramp Max Running Slope	8.333%	4.764°	1 : 12
10% Gradient Benchmark	10.000%	5.711°	1 : 10
45° Incline (1:1 Slope)	100.000%	45.000°	1 : 1

Grade uses horizontal run, not slope length. The ratio reports absolute steepness; the signed result separately identifies uphill or downhill. A slope value alone does not establish legal or design compliance.

ADA standards U.S. Access Board ramp guide FHWA Bridge Geometry Manual

Summary

Calculate grade percent, angle, elevation change, slope length, and gradient ratio (1:n) with explicit input modes and signed uphill/downhill direction.

How it works

Select your known calculation pair: rise & run, grade & run, angle & run, or rise & slope distance.
Choose your measurement unit (feet, meters, or generic units).
Enter positive numbers for uphill slopes or negative numbers for downhill slopes.
Click Calculate to compute grade percentage, slope angle, decimal slope, gradient ratio (1:n), and slope length.
Use the linked official references when a design must meet a particular standard or local code.

Use cases

Calculate vertical road grade percentage from surveyed rise and horizontal map distance.
Convert slope angles in degrees to roadway grade percentages and gradient ratios.
Determine required horizontal run or vertical elevation change for site grading.
Convert traveled slope distance (hypotenuse) to true horizontal run for plan drawings.
Compare the geometry with a project-specific road, drainage, or accessibility requirement.
Determine slope ratios (e.g., 1:100, 1:20, 1:12) for drainage and civil engineering layouts.

Frequently Asked Questions

Last updated: 2026-09-20 · Reviewed by Nham Vu