How this instrument works
Grade describes how steeply a surface climbs or falls over a horizontal distance, expressed as a percentage rather than an angle. A 3% grade means the surface rises 3 feet for every 100 feet of horizontal run — the vertical change divided by the horizontal distance, multiplied by 100 to turn the ratio into a percentage that's easy to compare across a site plan.
This is the figure used almost everywhere in site work and civil design: drainage swales are graded a minimum percentage so water actually flows toward an outlet instead of pooling, driveways have maximum grades before they become impractical for vehicles in winter, and accessibility codes cap ramp grades at a strict percentage so a ramp stays usable rather than becoming a slide.
Grade percentage is easy to confuse with a slope angle in degrees, but they are not the same number — a 100% grade is a 45-degree angle, not vertical, because grade compares rise to horizontal run while an angle measures rotation from horizontal. This instrument reports grade as a percentage only, which is the figure almost every grading plan, spec sheet and building code actually calls for.
- Enter Rise (ft) — the vertical change in elevation between your two points; use a negative number for a downhill run if your project needs signed grades.
- Enter Run (ft) — the horizontal distance over which that rise occurs, measured flat, not along the slope itself.
- Read Grade (%) directly — it recalculates the instant either field changes.
- Run must be greater than zero; a horizontal distance of zero has no defined grade, since you'd be dividing by nothing.
Worked example — 3 ft of rise over a 100 ft run
Enter 3 into Rise (ft) and 100 into Run (ft) — three feet of elevation change over a hundred-foot horizontal distance, a common minimum grade for a drainage swale. Grade (%) reads 3.0: (3 ÷ 100) × 100 = 3.0% exactly.
A 3% grade is steep enough to move surface water reliably toward an outlet but shallow enough to walk or drive across comfortably — which is exactly why 3% shows up so often as a minimum grading spec on residential and commercial site plans.
Questions
What's the difference between grade percentage and slope angle in degrees?
Grade compares rise to horizontal run and multiplies by 100, while an angle measures rotation from horizontal in degrees — they use different math and don't scale the same way. A 100% grade is only a 45-degree angle, not vertical, because at 45 degrees the rise and run are equal, giving a ratio of 1, or 100%. This instrument reports grade as a percentage, since that's the figure used on most grading plans and codes.
What grade does a ramp need to meet accessibility requirements?
In the United States, the ADA Standards for Accessible Design cap a ramp's running slope at 1:12, which works out to roughly 8.33% grade — meaning no more than 1 inch of rise for every 12 inches of horizontal run. This instrument calculates grade generically for any rise and run; check your local code or the ADA standards directly for the exact figure that applies to a specific accessibility project.
What's a typical maximum grade for a driveway?
Residential driveway guidelines commonly recommend keeping grades under roughly 15–20% for reasonable vehicle traction, with steeper sections becoming difficult or unsafe in snow and ice; many municipal codes cap driveway grades even lower. Because these limits vary by jurisdiction and vehicle type, treat this instrument's output as the raw grade figure to check against your specific local requirement, not as a pass/fail verdict on its own.
Can rise be negative for a downhill grade?
Yes — enter a negative value for Rise (ft) if you're measuring a downhill run, and Grade (%) will come back negative to match, since the formula is a plain division that preserves sign. A negative grade simply means the surface falls rather than climbs over the measured run; the magnitude of the percentage works the same way in either direction.
Why can't run be zero?
Because grade is rise divided by run, and dividing by zero has no defined result — a run of zero would mean the two points being compared are at the same horizontal position, which isn't a slope at all. This instrument requires a run greater than zero and will not compute a grade otherwise.