Slope, Grade & Percent Calculator
Convert any incline between rise-over-run, percent grade, degrees, 1:x ratio and per-mille, with the rise and slope length over a distance you choose.
The same slope in the form the drawing, the level, the drainage spec or the ramp note uses — and how much it climbs over a given distance — with the conversions made explicit.
Example: A rise of 1 over a run of 12 is 8.33 %, 4.76°, 1:12, 83 ‰; over 12 units the sloping length is 12.04. A 30° bank is 57.7 % or 1:1.73.
One incline,
five ways to write it.
How the forms relate, where percent and degrees part company, and why no maximum slope is given here.
Rise, run and the four notations
Every notation starts from the gradient, rise divided by horizontal run. Percent grade is that × 100 (a 1 in 12 slope is 8.33 %); per-mille is × 1,000, used for drains and railways; the ratio 1 : x writes it as one unit up for x units along (1:12); and the angle is its arctangent (4.76°). Enter whichever you have and the others are derived exactly. The run is measured horizontally, not along the slope — a common source of error when a tape is laid on the ground.
Percent is not degrees
The two scales only look alike at small slopes (a 5 % grade is 2.86°). At 45° the grade is 100 %, and a cliff at 89° is over 5,700 % — percent keeps growing while the angle approaches 90°. The page flags anything past 45° so a figure typed in the wrong box is noticed. Rise and run may be in any unit as long as it is the same one; the optional distance uses that unit too.
Slope length and rise over a distance
Over a horizontal distance d the incline climbs g × d and the sloping length is d × √(1 + g²) — the length of pipe, ramp surface or handrail rather than the plan length. Give a distance to see both; without one the page uses the run you entered, or 100 units for the other notations.
Why no limits are shown
Maximum ramp gradients, minimum drain falls, roof pitches for a given covering and road grades are set by the building code, accessibility standard, drainage regulation or road authority that applies to your project, and they differ by jurisdiction. This page converts; it does not judge. Nothing leaves the browser; the same four anonymous usage counts as the rest of the site apply.
SOURCES
- Trigonometric definitions: grade = tan θ, θ = arctan(rise ÷ run) — standard mathematics; ratio and per-mille are the same quantity written differently
Last reviewed 19 September 2026. How results are checked: How we verify.