Slope & Gradient Calculator

Understand grade as percent, angle and ratio

Road signs, trail profiles and engineering drawings describe slope in different ways. Percent grade is rise divided by horizontal run multiplied by 100, while the angle in degrees comes from the arctangent of the same ratio. A 1:n ratio expresses the same geometry in another familiar form.

Keep rise and run in the same unit before calculating. The result describes the average slope between two points; real terrain or roads can contain steeper short sections that an average does not reveal.

When this tool is useful

Use Slope & Gradient Calculator when the question matches the method the page actually uses. Typical workflows include:

• Compare two or more scenarios involving gradient calculator without creating an account or installing desktop software.
• Use the output as a planning or teaching reference, then move to an official or specialist source if the result affects legal, safety, engineering or financial decisions.
• Run the same workflow for locations in different countries while keeping units and assumptions consistent.

Worked examples

These examples are meant to show how to interpret this kind of output, not to replace the values produced from your own inputs.

• Eye height near sea level — With eyes about 1.7 m above sea level, the refracted-horizon estimate is roughly 5 km.
• 100 m viewpoint — At 100 m elevation above a clear horizon, the estimate increases to roughly 39 km.
• Antipode example — New York's antipodal coordinate is approximately -40.71, 105.99.

How to interpret the result

The most common errors come from using a correct result to answer the wrong geographic question. Keep these points in mind for Slope & Gradient Calculator:

• Treat climate and hardiness outputs as 30-year character, not this year's weather: a zone tells you what winters usually allow, and microclimates — walls, slopes, urban heat — shift a real garden half a zone either way.
• Remember that elevation models see bare terrain: no buildings, no forest canopy. A line-of-sight 'clear' verdict can still be blocked by a wood, and a horizon distance assumes open ground — treat results as the terrain baseline, then add land cover from local knowledge.

Limits & appropriate use

Terrain intelligence carries one dominant limit: the model sees bare earth at ~90 m spacing with metres of vertical error, and is blind to canopies, walls and wires. Every downstream answer inherits it — profiles show terrain truth with noisy amplitude, line-of-sight verdicts are pending trees, horizons assume open ground, and solar radiation averages assume an unshaded panel. The second limit is temporal: climate letters and hardiness zones are thirty-year character, not this year's behaviour, and seismicity is a mood, not a hazard model. Each result here is printed with its recipe precisely so these boundaries travel with the number.

The value proposition is screening-grade truth at zero cost: orientation for sites, gardens, antennas, shoots and curiosity, with the upgrade points clearly marked. When money or safety attaches to the answer — tower siting, flood insurance, structural shading, avalanche terrain — the escalation is professional: licensed survey, certified shade studies, regulatory flood determinations and geological hazard services. A good free tool makes that ladder visible instead of pretending to be the top of it.

• Construction and tower siting → licensed topographic survey.
• Flood decisions → regulatory determinations (FEMA/FIRM in the US).
• Solar finance → certified shade and production studies.

Data & methodology

Grade = rise/run × 100; slope angle = atan2(rise, run). Elevation and radiation use Open-Meteo's open API on Copernicus/ERA5 datasets; visibility math adds standard refraction (k = 0.13). US hydrology/flood layers come from USGS and FEMA public services.

For source details, licences and model limitations, see Data Sources and Methodology.

Key terms worth knowing

Antipode

The diametrically opposite point; latitude flips, longitude shifts 180°.

Köppen class

The letter-code climate system from temperature/precipitation thresholds.

Go deeper: guides & original studies

Use these resources when you need the reasoning behind the calculation, a comparison with another geographic method, or an example of the same approach applied across a dataset.

Related tools

If this page answers only part of your question, these tools use a nearby but different method or dataset.