Google Earth Slope Angle: How to Measure Terrain

Google Earth does not provide a universal, direct slope-angle reading for every point, but you can estimate terrain steepness by measuring horizontal distance and elevation change, then calculating the angle. Enter those values in a slope-angle calculator to get the result in degrees; Google Earth’s terrain and elevation data are approximate, so treat the answer as an estimate rather than a survey measurement.

Formula

The slope angle is the inverse tangent of the elevation change divided by horizontal distance: θ = arctan(h / d). The calculator uses atand, which returns the result in degrees. Grade is a related measure: grade (%) = 100 × h / d.

• θ is the slope angle in degrees.
• h is the vertical elevation change, in metres in this calculator.
• d is the horizontal distance along the map, also in metres.
• Grade is the rise divided by horizontal run, expressed as a percentage.

Use horizontal distance rather than the length measured along the sloping ground. The formula assumes the terrain can be represented by one straight rise over one straight run. If elevation decreases in the direction of travel, use the magnitude of the change to report steepness, or retain a negative sign separately to show downhill direction.

Worked Example

With the default inputs, elevation change is 100 m and horizontal distance is 500 m.

1. Divide rise by run: 100 ÷ 500 = 0.2.
2. Take the inverse tangent and convert to degrees: arctan(0.2) ≈ 11.31°.
3. Calculate grade: 100 × 0.2 = 20%.

The result is a slope angle of 11.31° and a grade of 20%. These describe the same rise and run in different ways; 20% does not mean 20 degrees.

How to Measure a Slope in Google Earth

In Google Earth, identify the top and bottom of the section you want to assess, measure the horizontal distance between them, and obtain an elevation for each endpoint. The exact controls and displayed details can vary between the web version and the desktop application, and terrain availability depends on the location and data coverage.

1. Navigate to the terrain and zoom in enough to identify the endpoints. Keep the map view as close to top-down as practical so the selected route follows the ground rather than a perspective view.
2. Use the measuring tool to draw a line or path between the two points. Choose a distance unit you can convert consistently; this calculator expects metres.
3. Find the elevation at both endpoints using the available terrain or location information. Subtract the lower elevation from the higher one to get the elevation change.
4. Enter the elevation change and map distance above. For example, convert 0.5 km to 500 m before entering it if the elevation difference is in metres.
5. For a long or uneven route, divide it into shorter sections and calculate each separately. A single average can conceal steep pitches, ledges, and flatter stretches.

Google Earth’s elevation profile, where available for a measured path, can help show how elevation varies along the route. Read the profile as a sequence of terrain changes, not proof that every local feature is captured accurately. A path drawn across a hillside may also cross ridges or gullies, making its overall endpoint calculation a poor description of individual sections.

Angle, Grade, and Distance: What They Mean

Angle is measured in degrees from the horizontal. A level surface is 0°, and a vertical face is 90°. Grade is the vertical rise divided by horizontal run, multiplied by 100. Thus a 20% grade means 20 units of rise per 100 units of horizontal distance, not a 20° angle. In this example, 20% grade corresponds to about 11.31°.

Some maps and outdoor sources use “slope” to mean grade, while others mean angle. Check the unit before comparing figures. The calculation also differs if you use distance along the ground: the formula requires horizontal run. If you only know the sloping length, do not enter it as the horizontal distance; the resulting angle will be wrong.

Accuracy and Common Problems

A mathematically correct result can still be a poor description of real terrain if the input data are imprecise. Terrain elevation grids smooth or omit small landforms, and the location of a chosen point may not match the spot you intended. Measurement scale, map resolution, vegetation, buildings, and steep or narrow features can all affect an estimate.

• Mixing units: Convert both measurements to the same distance unit before dividing. For instance, use 30 m and 150 m, not 30 m and 0.15 km without conversion.
• Using the wrong distance: Measure horizontal map distance, not the distance traced over the sloping surface.
• Using endpoint averages on complex ground: A 500 m route may include a short very steep pitch even when its average angle is modest.
• Confusing percent with degrees: A 100% grade is 45°, while a 100° slope is not possible as an ordinary surface angle measured from horizontal.
• Over-interpreting decimals: A display such as 11.31° does not imply that the underlying terrain data are accurate to one-hundredth of a degree.

For construction, land surveying, engineering, or decisions where a small error matters, use suitable surveyed elevation data and professional measurement methods rather than relying on a map estimate. Google Earth is useful for exploration and rough comparisons, but it is not a substitute for a site survey.

When a Google Earth Slope Estimate Is Useful

An estimate can help compare broad terrain sections, understand whether a route climbs gradually or sharply, or identify places to investigate with better data. It is especially informative when paired with an elevation profile and several short measurements. For a hiking route, for example, calculate individual climbs rather than dividing the total climb by the full route length; the latter reports only an overall average.

Remember that slope angle alone does not determine whether a surface is safe or easy to travel. Surface material, loose rock, snow, water, vegetation, exposure, and route conditions matter too. A map-derived angle should not be treated as a safety assessment.

Frequently Asked Questions

Can Google Earth show slope angle directly?
It can provide terrain information and, in some versions or locations, elevation profiles, but it does not offer a dependable universal point-and-read slope angle for every hillside. Calculate an estimate from elevation change and horizontal distance.

How do I calculate slope angle from elevation and distance?
Divide the elevation change by horizontal distance, then take the inverse tangent: θ = arctan(h ÷ d). Use consistent units and report the angle in degrees if that is the desired unit.

Is a 20% slope the same as 20 degrees?
No. A 20% grade is a rise-to-run ratio of 0.2 and equals approximately 11.31°. A 20° angle corresponds to a steeper grade of about 36.4%.

Should I use the path distance or the straight-line distance?
Use the horizontal distance of the specific section being assessed. If the path curves, measure along the map path rather than using a shorter endpoint-to-endpoint shortcut, but split complex terrain into sections to avoid hiding steep parts.

How accurate is a Google Earth slope calculation?
The arithmetic can be precise, but the result is only as reliable as the selected points, horizontal measurement, and elevation data. Treat it as an approximation, especially for small or steep features.

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in h | Elevation change | m | 100 | 0
in d | Horizontal distance | m | 500 | 0
out angle | Slope angle | degrees | atand(h / d) | 2
out grade | Grade | % | 100 * h / d | 2