Elevation Grade Calculator

An elevation grade calculator returns percent grade, slope ratio, and angle from a measured rise and run. Grade is the rise divided by the run, in matching units, times 100. For drainage away from a foundation or a wheelchair ramp, it also compares the result with the IRC or ADA limit.

Last reviewed September 2026Method & sources Report an error

Not to scale.

Grade

5.00 %

Comparison

A 5.0% grade rises steadily over the measured run.

Breakdown
Grade	5.00%
Slope Ratio	1 in 20.0
Angle	2.86°

How to Calculate Elevation Grade

Grade as a percentage is `(Rise ÷ Run) × 100`, with rise converted to the same unit as run first (here, rise in inches ÷ 12 to get feet, matching the run). The slope ratio expresses the same relationship the way it's often written on plans. 1 in X means X feet of horizontal run for every 1 foot of rise. The angle in degrees is `arctan(Rise ÷ Run)`, useful for comparing against an angle-based spec instead of a percentage. When a specific purpose is selected, the calculated grade is compared against that use's own published minimum or maximum: IRC R401.3 requires land within 10 ft of a foundation to fall at least 6 in. over that distance for soil grading, or slope at least 2% if the surface is impervious (concrete, pavers). The ADA's accessibility standards (Section 405.2) cap a ramp's running slope at 1:12, or about 8.33%.

Example: 6 in. rise over a 10 ft run, checked against the drainage minimum

A 6 in. rise over a 10 ft run, checked against the drainage minimum: 1. Run in inches: 10 × 12 = 120 in. 2. Grade: (6 ÷ 120) × 100 = 5% 3. Slope ratio: 120 ÷ 6 = 20, so 1 in 20.0 4. Angle: arctan(6 ÷ 120) ≈ 2.86° 5. Comparison: 5% clears the IRC R401.3 minimum of 2% for impervious surfaces near a foundation This is also IRC's own reference example for soil grading (6 in. of fall in the first 10 ft). It works out to a comfortable 5%, well above the stricter 2% minimum that applies specifically to paved surfaces.

What Is Elevation Grade?

An elevation grade calculator converts a measured rise and run into the three common ways slope gets expressed: percent grade, a slope ratio (1 in X), and degrees. For two common regulated uses, drainage away from a foundation and a wheelchair ramp, it checks the result against the published code minimum or maximum for that specific purpose.

Elevation Grade: Pros and Cons

Pros

Gives all three common ways grade is expressed (percent, ratio, degrees) from one measurement, since different plans and specs use different conventions
Compares the calculated grade against a real, cited code threshold when a specific regulated use is selected, instead of leaving you to look up the number separately
Works for a rise or a fall (negative rise), catching the case where a foundation grade is sloped the wrong way

Cons

Doesn't measure the rise and run for you. Accuracy depends entirely on how the two measurements were taken
The drainage and ramp comparisons check against the general baseline requirement only. A specific ramp design also has rules around landings, handrails, and cross-slope that this calculator does not check
A percentage grade calculation is not itself an engineering or accessibility sign-off. For a permitted ramp or a drainage plan tied to a permit, have the final design reviewed by whoever has authority over that permit

Elevation Grade: What a Pro Checks

Grade land away from a foundation at least 2% if the surface is impervious (concrete, pavers) or with at least 6 in. of fall over the first 10 ft for soil, per IRC R401.3, since water can pond instead of draining away below that.
Keep a wheelchair ramp's running slope at or under 1:12 (about 8.33%), per ADA Standards Section 405.2. This calculator flags when a rise/run combination exceeds that maximum.

Frequently Asked Questions

How do you calculate percent grade from rise and run?

Divide the rise by the run (in the same units) and multiply by 100. A 6 in. rise over a 10 ft (120 in.) run is (6 ÷ 120) × 100 = 5%. Keep the units consistent. A common mistake is dividing inches of rise by feet of run without converting one of them first.

What slope does my yard need for drainage?

IRC R401.3 sets two figures. For soil, land within 10 ft of a foundation should fall at least 6 in. over that distance (about 5%). For an impervious surface such as concrete or pavers, the slope should be at least 2%. Where a lot line or wall prevents that much fall, a drain or swale is required instead.

What is the maximum slope for a wheelchair ramp?

1:12, or about 8.33%, per the ADA Standards for Accessible Design, Section 405.2. That means at least 12 in. of horizontal run for every 1 in. of rise. Existing sites with real space constraints have narrower exceptions allowing steeper short ramps, but 1:12 is the standard for new construction.

What's the difference between grade, slope ratio, and angle?

They're three ways of describing the same rise-over-run relationship. Grade (percent) and slope ratio (1 in X) are both common on civil and landscape plans. Grade is easier to compare against a code minimum, while a ratio is often easier to picture and stake out on site. Angle in degrees is more common in engineering and surveying contexts.

Can I use this for a roof or a driveway instead?

The percent grade and slope ratio math applies to any rise-over-run situation, but the two built-in comparisons here (drainage and ADA ramps) are specific to those two uses. For roof slope specifically, see the Roof Pitch Calculator, which uses the roofing industry's own rise-per-12-inches convention.

Sources

Lawn & Landscaping