JoseFitani
⛰️ Elevation & Terrain

Slope Calculator

Calculate the slope of a terrain or ramp from rise (vertical) and run (horizontal) distances.

This page explains how the slope calculator works, the data and formulas behind it, and how to interpret the result. SRTM (Shuttle Radar Topography Mission) was flown in 2000 and covers 80% of Earth's land surface with 30 m resolution and ~16 m vertical accuracy. In the United States, USGS 3DEP 10 m data is used for better accuracy. The tool is one of 329 free, open tools on JoseFitani for maps and geography. It runs in your browser with no sign-up needed. Use the search field or click the map to drop a pin - the tool uses queries to the Open-Elevation API backed by SRTM 30 m and country-specific DEMs and returns the result in seconds. Below you'll find a step-by-step guide, real use cases, the methodology, FAQs, and data sources.

Important notice

Slope figures are approximate and derived from the numbers you enter. They are for general information only — verify on site before relying on them for construction, drainage, or safety-related decisions.

Slope
6.0 %
rise ÷ run × 100
Slope angle
3.4°

Formula: slope % = (rise in metres ÷ horizontal distance in metres) × 100; angle = arctan(rise ÷ run). Uses straight-line horizontal distance, not slope distance.

How to use this tool

1
Enter your input

Type your query, paste coordinates, or click on the map. The tool uses queries to the Open-Elevation API backed by SRTM 30 m and country-specific DEMs to process your input locally in the browser.

2
View the result

The result appears instantly with the map showing your location. You can adjust by clicking elsewhere or searching a new place.

3
Copy or share

Click Copy to save to clipboard, or Share to send a direct link with the exact inputs.

What people use this tool for

Driveway design on hills

Homeowners building on a slope need the driveway gradient before pouring concrete. A 20 percent grade ices over dangerously and strains car transmissions, so the number drives the design. If the measured slope is too steep, the route gets lengthened with switchbacks.

Example: A family building above Ooty measures the rise from the road to the house plot and redesigns the driveway as two gentler legs instead of one steep shot.
Wheelchair ramp compliance

Accessibility guidelines cap ramp slopes, commonly at a 1:12 ratio, to keep them safely usable. Measuring an existing ramp's rise and run shows whether it passes. A failed reading means the ramp must be lengthened or rebuilt.

Example: A cafe owner in Pune measures the entrance ramp and finds 1:9, so the ramp gets extended by a metre to meet the recommended ratio.
Ski run grading

Resort teams classify runs by steepness: gentle beginner slopes sit near single-digit grades while expert runs push past 40 percent. Measuring a new cut confirms which colour marker it earns. The angle reading also guides grooming and avalanche-control decisions.

Example: A ski patrol in Gulmarg measures a new off-piste line at 38 percent and marks it advanced rather than intermediate.
Ghat road assessment

Drivers and fleet operators check the steepest grades on mountain highways before sending loaded trucks through. A sustained 12 percent climb overheats brakes on the way down and crawls on the way up. Knowing the grades shapes gear choice and rest stops.

Example: A logistics manager checks the ruling gradient of a Western Ghats route and reroutes heavy tankers onto a longer but gentler pass.

How it's calculated

Slope percent = (rise / run) x 100. Slope angle = arctan(rise / run).

The calculation runs in your browser - no data is sent to our servers. Map tiles come from OpenStreetMap (ODbL license), geocoding uses Nominatim (1 request/second limit), and elevation uses the Open-Elevation API backed by SRTM data. All are free, open services.

All calculations use the WGS84 datum (EPSG:4326), the same as GPS. For other datums (NAD27, NAD83, ETRS89), a separate conversion is needed. The difference is typically under 1 metre - negligible for most uses but important for survey-grade work.

The formulas match those in professional GIS software (QGIS, ArcGIS, Global Mapper), just in a browser-friendly form. For sub-metre accuracy, use professional software with ellipsoidal calculations. Results are shown in multiple units: km and miles for distance, km²/m²/hectares/acres for area, metres and feet for elevation. Conversion factors are exact (1 mile = 1.609344 km), so the only error source is input precision.

Related tools and resources

For more tools in this category, explore the related tools listed below. Each tool includes full documentation, examples and FAQs. Explore related tools in our Elevation category for complementary functionality. See the Tools index for all 329 tools, or read our blog for in-depth articles on geography and maps.

Frequently asked questions

What is a 100% slope?

A 100% slope equals a 45° angle.

What is the difference between percent grade and degrees?

Percent grade is rise divided by run times one hundred, while degrees measure the actual angle of the surface. They are related by the tangent: a 100 percent grade equals 45 degrees, and a 10 percent grade is about 5.7 degrees. Road signs use percent grade; roofers and skiers often think in degrees.

What do rise and run mean exactly?

Rise is the vertical change in height between the two ends, and run is the horizontal distance covered. Both must use the same unit, metres and metres or feet and feet, for the ratio to work. Measuring the sloped distance along the ground instead of the horizontal run is the most common mistake.

What does a 1:12 ratio mean?

It means one unit of vertical rise for every twelve units of horizontal run, which works out to about an 8.3 percent grade. Ratios are the language of ramps, roofs, and drainage because they read directly as construction dimensions. A 1:12 ramp that rises half a metre must run six metres.

Can slope be negative?

Yes. A negative grade simply means the ground falls in the direction of travel instead of rising. A minus 8 percent downhill is the same steepness as a plus 8 percent uphill. Cyclists and drivers care about the sign; the math is identical either way.

What grade can cars handle?

Most passenger cars climb sustained grades around 15 to 20 percent without trouble, and the steepest paved public roads reach about 30 percent. Beyond that, traction, cooling, and brake fade become the limits rather than engine power. Loaded trucks prefer to stay under 8 to 10 percent on long climbs.

How do I measure rise and run in the field?

For short distances, a spirit level, a tape measure, and a ranging pole give both numbers directly. For longer slopes, take the elevation difference between two GPS points as the rise and the map distance between them as the run. This calculator turns either pair into grade, ratio, and angle.

Is percent grade the same as the angle in radians?

No. Radians measure angle like degrees do, just in different units, while percent grade measures the tangent of the angle. Confusing them causes real errors: a 45-degree slope is 100 percent grade, not 78.5 percent. Use the angle column when you need degrees and the grade column for road-style figures.

Does this calculator need the internet?

No. Slope math is simple division and trigonometry that runs entirely in your browser. Enter rise and run with the page loaded and you get grade, ratio, and angle instantly, with or without a connection.

Data sources & methodology