Slope Calculator
Work out gradient, percentage grade, angle and roof pitch instantly — from two points, a rise-and-run measurement, or an angle you already know.
What slope actually means
Slope describes how much a surface rises or falls over a given horizontal distance. Every builder, roofer, landscaper and civil engineer ends up expressing the same physical tilt in a handful of different ways — as a ratio, a percentage, an angle, or a roofer’s “x in 12” pitch — and the calculator above converts freely between all of them. Below is a plain guide to what each figure means and when it’s the right one to use.
The core formula
However you measure it, slope always comes back to the same relationship between vertical change and horizontal distance:
“Rise” is the vertical difference between your two points; “run” is the horizontal distance between them. If you know two coordinates instead, the same idea applies:
A slope of 0.3, for example, means the surface climbs 0.3 units for every 1 unit travelled horizontally — regardless of whether those units are metres, feet or miles, as long as both measurements use the same unit.
Turning slope into a percentage
Percentage grade is the figure you’ll see on road signs and gradient markers. It’s simply the slope multiplied by 100:
A 10% grade rises 1 metre for every 10 metres travelled. Anything above roughly 8–10% is considered steep for a road or driveway, while wheelchair ramps in the UK are generally limited to a maximum of 1 in 12, or about 8.3%.
Slope as an angle
Where a ratio or percentage tells you how steep something feels underfoot, an angle in degrees is what a surveyor’s level or an inclinometer actually reads. To convert:
A 45° angle corresponds to a slope of exactly 1 (a 100% grade) — rise and run are equal. Anything steeper than 45° means the rise is greater than the run.
Roof pitch: the “x in 12” system
Roofers in the UK and US traditionally express slope as a ratio out of a 12-inch (or 12-unit) run, written as “6 in 12” or “6:12”. It’s the same underlying rise-over-run calculation, just scaled so the run is always 12:
A “4 in 12” roof is fairly shallow and common on modern extensions; “9 in 12” or steeper is a traditional pitched roof that sheds snow and rain quickly but needs more roofing material and a steeper safe-working assessment for anyone up there.
Quick reference: common slopes
| Context | Typical slope | As a percentage | As an angle |
|---|---|---|---|
| Wheelchair ramp (max, UK Building Regs Part M) | 1 : 12 | ~8.3% | ~4.8° |
| Driveway (comfortable) | 1 : 10 to 1 : 20 | 5–10% | 3–6° |
| Flat roof drainage fall | 1 : 40 to 1 : 80 | 1.25–2.5% | <1.5° |
| Low-pitch roof | 4 : 12 | ~33% | ~18.4° |
| Standard pitched roof | 6 : 12 | 50% | ~26.6° |
| Steep pitched roof | 12 : 12 | 100% | 45° |
| Staircase (typical rise/going) | ~0.85 : 1 | ~85% | ~40° |
Where slope calculations matter on site
Drainage and land grading
Ground that’s perfectly flat holds water, so paths, patios and land around a building are always given a slight fall away from structures — typically 1:40 to 1:60 — enough to shed water without being noticeable underfoot. Getting this wrong is one of the most common causes of damp at the base of a wall.
Ramps and accessibility
Under UK Building Regulations Approved Document M, permanent ramps are generally limited to a maximum gradient of 1:12, with shallower ratios preferred wherever the available run allows it, plus level landings at intervals. Checking the achievable ratio before construction avoids a ramp that fails building control sign-off.
Roofing and materials
A roof’s pitch determines which covering materials can be used — very low-pitch roofs generally need a fully waterproof membrane rather than overlapping tiles, since shallow pitches don’t shed water fast enough to rely on overlap alone. Manufacturers publish a minimum pitch for each product, so converting a measured rise and run into a pitch is usually the first check before ordering materials.
Excavation and retaining structures
The angle of a cut slope affects its stability — different soil types have a maximum safe angle before they’re prone to collapse. Expressing a proposed cut as a ratio or angle makes it straightforward to compare against a geotechnical recommendation.
This calculator gives you the geometry — the ratio, percentage, angle and pitch. It doesn’t replace site-specific advice from a structural engineer, building control officer, or roofing manufacturer’s specification for load, material choice, or regulatory compliance.
How to use the calculator
- Two Points — use this if you’ve measured or plotted coordinates, for example from a level survey or a drawing.
- Rise & Run — the quickest option if you’ve simply measured a vertical height and a horizontal distance with a tape measure.
- Angle — use this if you already have a reading from an inclinometer, digital level, or protractor and want the equivalent ratio, percentage or pitch.
All three modes return the same six figures — slope as a decimal, gradient as a ratio (1 in x), percentage grade, angle in degrees, roof pitch, and the straight-line distance between the two points — so you can quote whichever format the job requires.