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Slope Percent to Degrees Calculator

Convert a percentage gradient into degrees for setting out drainage, ramps and driveways.

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  • Every formula cited
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Imperial · sales tax
The gradient as a percentage — rise divided by horizontal run, times 100.

A 2% fall means 2 units of drop over 100 units of run, which is the common minimum for surface drainage away from a building.

Slope angle

1.146 °

High confidence

Angle = arctan(percent ÷ 100). A larger ratio denominator means a gentler slope, while a larger percentage means a steeper one — the two run in opposite directions.

Then change the inputs to see how far the answer moves.

Show calculation logic

How this was calculated

Formula source(s)

  • Slope percentage = (rise / run) x 100; angle = arctan(rise / run)
  • ADA maximum running slope for a ramp is 1:12, which is 8.33% or about 4.76 degrees

Inputs used

Gradient (%)
2
Final result1.15 °

Confidence note: Angle = arctan(percent ÷ 100). A larger ratio denominator means a gentler slope, while a larger percentage means a steeper one — the two run in opposite directions.

1.15°10022 % · 1.15°

Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.

Sources checked 2026-08-26 · in the site-wide review of 2026-09-06 · v1.0.0

Regulatory standards & verification citations2
  1. Slope percentage = (rise / run) x 100; angle = arctan(rise / run)
  2. ADA maximum running slope for a ramp is 1:12, which is 8.33% or about 4.76 degrees
Cite this page

Your workspace

Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Drainage falls, ramp gradients and driveway slopes get expressed as percentages, ratios and degrees depending on which trade or standard is speaking, and this converts the first into the last. For the shallow angles that most site work involves, the percentage and the angle track each other closely — two percent is 1.15 degrees — but they diverge sharply as things steepen, so the approximation should not be carried into roof work. The genuinely confusing part is that ratios run the other way: a 1:12 ramp is steeper than a 1:20 one, while 8% is steeper than 5%. Keeping straight which convention a drawing uses prevents a fall being set out backwards.

How to calculate slope percent to degrees in 2 steps

  1. Gradient (%)The gradient as a percentage — rise divided by horizontal run, times 100.
  2. Slope angleThe tool computes the slope angle from those figures and shows the formula, its sources, and a confidence rating alongside it.

Slope Percent to Degrees at common values

Page defaults, not your figures above.

Gradient (%)Slope angle (°)
10.573
1.50.859
21.15
2.51.43
52.86
8.334.76
105.71
158.53
2011.3

Frequently asked questions

Is percent the same as a 1-in-X ratio?
Related but inverted. A 1:12 ratio is one unit of rise over twelve of run, which is 8.33%. Divide 100 by the percentage to get the ratio denominator, and remember that a larger ratio number means a gentler slope while a larger percentage means a steeper one.
What gradient does surface drainage need?
Commonly a 2% minimum fall away from a building for paving and hard landscaping, though local requirements vary and specific finishes have their own minima. Too flat and water ponds; the tolerance on a long run is what usually causes the problem.
Why do ramps use ratios instead?
Because accessibility standards were written that way and the ratio is easier to check on site with a level and a measure. A 1:12 maximum running slope is the familiar figure, equal to 8.33% or 4.76 degrees.
Why does 100% come out as 45 degrees and not vertical?
Because a percentage is rise over run, not a share of a right angle. At 100% the rise equals the run, which is 45 degrees; 200% is about 63.4 degrees, and a vertical face is no finite percentage at all. That is why percentages stop being useful on steep ground and roof work changes to pitch or degrees.
Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — a confirmed fix gets a permanent check of its own, so the same mistake cannot come back.