How do I calculate the grade of a slope?

Divide the rise (the vertical change) by the run (the horizontal distance) and multiply by 100 for a percentage. A drop of 2 ft over 50 ft of run is 2 ÷ 50 = 0.04, or a 4 percent grade (0.5 m over 12.5 m is the same 4 percent). This tool takes your rise and run and reports the grade, the angle and the ratio at once.

What is the difference between grade, angle and ratio?

They are three languages for the same steepness. Grade is rise over run as a percent, the angle is that ratio in degrees (the arctangent of rise ÷ run), and the ratio is written like 1:25, meaning one unit up for every 25 along. Earthworks talk in percent, surveyors in ratios, and a level or inclinometer reads degrees.

What grade do I need for drainage?

This tool reports whatever slope you enter — it does not prescribe a minimum, because the right fall depends on the surface, the pipe and your local rules. A common rule of thumb for surface drainage is a fall of around 1 to 2 percent away from a building, but confirm the figure your job actually requires with the relevant standard.

How much does a slope drop over a given distance?

Multiply the grade fraction by the distance. At a 4 percent grade, over 30 ft the drop is 0.04 × 30 = 1.2 ft; over 10 m it is 0.4 m. Enter a distance in the projection field and the tool works out the fall for you, in the same units as your run, which is handy for setting string lines and marking batter boards.

Slope grade calculator

This reports the slope you enter, in percent, degrees and ratio. It does not set the grade your job needs — minimum falls for drainage, ramps, driveways and pipes are fixed by the relevant standard and your authority, not by this tool. Check the required figure against that standard before you cut or fill to it.

Enter the rise and the run — any matching units — and the tool gives the grade as a percentage, the angle in degrees and the reduced ratio, all from the one relationship of rise over run. Add a distance in the last field and it also tells you how far the ground drops over that run at this grade.

Ejemplo resuelto

A yard that falls 2 ft over a 50 ft run is a grade of 2 ÷ 50 = 0.04, or 4%. As an angle that is arctan(0.04) ≈ 2.29°, and as a ratio it is about 1:25. Over a 30 ft path at that same grade the drop is 0.04 × 30 = 1.2 ft — the number you set your string line to.

In metric: a fall of 0.6 m over a 15 m run is 0.6 ÷ 15 = 0.04, the same 4% and 2.29°. Over a 9 m path the drop is 0.04 × 9 = 0.36 m, 360 mm below the start.

En la obra

Setting a string line for a pipe run. The drawing calls for a 1.5% fall over 80 ft of trench. Drop is 0.015 × 80 = 1.2 ft — 14⅜ in — from the upstream invert to the downstream one. Set the far batter board 14⅜ in lower than the near one, then check every 20 ft: at 20 ft the pipe should be 3.6 in down, at 40 ft 7.2 in. The percentage comes off the drawing; the inches come off this page. In metric the same 1.5% over 24 m of trench is 0.015 × 24 = 0.36 m — 360 mm — and the pipe drops 90 mm every 6 m.

Grading away from a foundation. The landscape plan says 5% for the first 10 ft. That is 0.05 × 10 = 0.5 ft — 6 in of fall — so the grade at the edge of the bed is 6 in lower than at the wall (5% over 3 m is 150 mm). The "drop over a distance" field is exactly this: type the plan's grade as rise-over-run and the distance you are checking.

Reading a laser or transit. Two shots 50 ft apart read 4.62 and 5.37 on the rod. The ground fell 0.75 ft in 50: 0.75 ÷ 50 = 1.5%, a 1:67 slope, 0.86°. Whether that is enough is the drawing's business — the tool tells you what is there.

Pruebe un ejercicio

Quick referencefor grade

Pendiente: rise ÷ run × 100
1%: 1 ft per 100 ft · about ⅛ in per foot · 10 mm per metre · 0.57°
2%: ¼ in per foot · 20 mm per metre · 1:50 · 1.15°
Ratio to percent: 1:N = 100 ÷ N % — 1:25 = 4% · 1:12 = 8.3% · 1:4 = 25%
Percent to degrees: 5% = 2.9° · 10% = 5.7° · 25% = 14° · 100% = 45°
Caída: grade (as a decimal) × distance — 2% over 30 ft = 0.6 ft = 7.2 in · 2% over 10 m = 0.2 m = 200 mm

Mistakes to catchbefore you trust the number

Measuring the run along the slope with the tape on the ground — the run is horizontal; on a 10% grade the two differ by half a percent, on a steep bank it is a lot more.
Typing a rise in inches against a run in feet; the grade formula divides one by the other, so both must be in the same unit.
Reading a 2% fall as 2 in per foot — it is about ¼ in per foot; the tool's drop-over-distance line shows the real figure.

What an inspector looks forthe building or grading inspector, at the drainage review

On this part of the job

Ground falling away from the building for the distance and at the fall the code requires — look both figures up; they are short and specific.
That downspouts and sump discharge are carried clear and released where the plan allows, not onto a neighbour or back against the wall.
Swales and drainage routes as drawn, with positive fall the whole way and no flat spot holding water.
Walk, drive and ramp surfaces within the cross-slope and running-slope limits that apply to them.
Final grade against the approved elevations, particularly where the site meets a lot line.

Have this ready

The grading plan with elevations.
A level and rod, or a laser — a slope argued from eye never wins.

Every figure an inspector measures against comes from the code your jurisdiction has adopted, the stamped drawing, or the manufacturer's printed instructions — so none of them are printed here. Look the number up in your own book, type it into the tool, and the arithmetic is yours.

La fórmula

grade% = (rise ÷ run) × 100 · angle = arctan(rise ÷ run)

Rise over run is a pure ratio, so its units cancel and the grade is the same whether you measured in feet or metres. Multiply the ratio by 100 for a percent, take its arctangent for the angle, and invert it for the 1:x ratio. The drop over a distance is simply that ratio times the distance.

Preguntas

How do I calculate the grade of a slope?: Divide the rise (the vertical change) by the run (the horizontal distance) and multiply by 100 for a percentage. A drop of 2 ft over 50 ft of run is 2 ÷ 50 = 0.04, or a 4 percent grade (0.5 m over 12.5 m is the same 4 percent). This tool takes your rise and run and reports the grade, the angle and the ratio at once.
What is the difference between grade, angle and ratio?: They are three languages for the same steepness. Grade is rise over run as a percent, the angle is that ratio in degrees (the arctangent of rise ÷ run), and the ratio is written like 1:25, meaning one unit up for every 25 along. Earthworks talk in percent, surveyors in ratios, and a level or inclinometer reads degrees.
What grade do I need for drainage?: This tool reports whatever slope you enter — it does not prescribe a minimum, because the right fall depends on the surface, the pipe and your local rules. A common rule of thumb for surface drainage is a fall of around 1 to 2 percent away from a building, but confirm the figure your job actually requires with the relevant standard.
How much does a slope drop over a given distance?: Multiply the grade fraction by the distance. At a 4 percent grade, over 30 ft the drop is 0.04 × 30 = 1.2 ft; over 10 m it is 0.4 m. Enter a distance in the projection field and the tool works out the fall for you, in the same units as your run, which is handy for setting string lines and marking batter boards.

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