Slope and Grade Calculator

Turn rise and run into percent grade, ratio and angle, or find how much fall you need for a target grade.

What Do You Want to Find?
Height change. Use feet? Multiply by 12.
Horizontal distance, not along the slope.
Fractions and decimals both work.
–
Grade
Rise
Run
Ratio
Angle
Per foot
Slope length
Compared With

Saved Slopes

Items you add are saved in this browser.

NameRiseRunGradeRatioAngleRemove

How to Calculate Slope and Grade

Grade is rise divided by run, as a percentage. Run is the level distance, the way it shows on a plan, not the length along the ground. Keep both in the same units before dividing.

Grade (%) = rise ÷ run × 100
Angle = arctan(rise ÷ run)   Ratio = 1 : (run ÷ rise)

Slopes are written several ways. A 1:12 ramp rises 1 unit for every 12 of run (8.33%). Earthwork slopes are usually written run to rise, so a 3:1 bank goes 3 feet out for every foot up (33.3%). Drainage is often written in inches per foot: ¼″ per foot is about 2.08%.

Worked Example

Common Slope Limits

UseGradeSource

Check your local code and the current edition adopted where you build; some jurisdictions amend these.

Grade, Ratio and Angle

GradeRise : RunAngleInches per Foot

Tips

Percent grade and degrees are not the same: a 100% grade is 45°, not 90°. To lay out a slope on site, set a string level between two stakes and measure down from it; the drop over the string length gives the rise.