Slope & Grade Calculator
Convert any slope between rise/run, grade percent, angle in degrees, and ratio form (1:12) in one step — so you can check an ADA ramp, set a roof pitch, or grade a driveway against the numbers your code or drawing calls for.
How to Use
- Enter a rise and a run (in the same units) to define the slope — for example 12 in of rise over 144 in of run.
- Or skip rise/run and type a grade percent directly if that is the number you already have.
- Or type an angle in degrees if your drawing or instrument gives the slope as an angle.
- Or enter a ratio in 1:N form, such as 1:12 for an accessible ramp.
- Read all four forms at once and check them against the common-slope reference cards below.
Show Work
Common slopes
About the Slope & Grade Calculator
Working on building, materials estimation and site work? The Slope & Grade Calculator is a free browser tool that gives you the answer in seconds. Convert any slope between rise/run, grade percent, angle in degrees, and ratio form (1:12) in one step — so you can check an ADA ramp, set a roof pitch, or grade a driveway against the numbers your code or drawing calls for.
How it works
Put each value in its box and read the answer as you go. Because it recalculates live, you can play with the inputs to see how each one moves the result — handy for checking your own working or planning ahead. Everything happens on your device, so it is fast and private.
Want the deeper story? The Knowledge Base explains the ideas behind the tools in more detail.
Frequently Asked Questions
What slope makes an ADA-compliant ramp?
The maximum running slope for an accessible ramp is 1:12, which is 8.33% or about 4.76 degrees. Anything steeper needs to be re-thought — a longer run, switchbacks, or a lift. Each ramp run can rise at most 30 in before a level landing is required, and runs need handrails when the rise exceeds 6 in.
How do I read a roof pitch like 4/12?
Roof pitch is rise over a fixed 12 in of run, so 4/12 means the roof climbs 4 in for every 12 in across — enter rise 4 and run 12 here. That works out to a 33.3% grade and about 18.4 degrees. Below 4/12 most shingles need extra underlayment; 9/12 and steeper is considered a steep-slope roof.
What is the difference between grade and angle?
Grade is the rise expressed as a percent of the horizontal run (rise ÷ run × 100), while angle is the same slope measured in degrees from level. They are not the same number: a 100% grade is a 45-degree angle, not 90. Use grade for roads and drainage and degrees when you are setting a saw or transit.
What slope do I need for drainage?
A flat roof or paved area needs a minimum of about 1:50 (2%) to shed water reliably, and finished grade around a foundation should fall at least 6 in over the first 10 ft (5%) to carry water away. Too little slope ponds water; too much erodes. When in doubt, build in a little extra fall.
How do I convert a ratio like 1:12 to a percent?
Divide the rise by the run and multiply by 100: 1 ÷ 12 = 0.0833, or 8.33%. A 1:20 ratio is 5%, and 1:4 is 25%. This tool does the conversion automatically — type the ratio in the 1:N box and the grade, angle, and rise/run all fill in.
How do I use the Slope & Grade Calculator?
Just type your numbers. The answer shows up right away — there is no button to press. Change anything and it updates by itself.
Do I need to install or sign up for anything?
Not at all — it runs in the browser with nothing to install and no account. After it loads once, it even works without an internet connection.
Is my information private?
Yes. Everything happens in your browser. Nothing you type is sent to a server or saved anywhere.
Common Use Cases
Checking a wheelchair ramp
Confirm a proposed ramp meets the 1:12 (8.33%) accessibility limit before you frame it.
Setting a roof pitch
Translate a 4/12 or 9/12 roof pitch into degrees and percent for cuts, ordering, and material selection.
Grading for drainage
Lay out a driveway, patio, or finished grade that falls enough to drain without being a trip or erosion hazard.
Reading a survey or plan
Convert a grade or ratio on a drawing into the degrees you can dial into a saw, transit, or laser.
Sizing a deck or ground ramp
Work backward from a target slope to the run you need over a known rise so the ramp fits the space.
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