How to Measure Slope Angle: 5 Simple Methods

Updated 11 November 2026 · Standard formula, shown below

This guide shows you how to measure the angle of a slope—whether you’re working on a driveway, a roof, a hiking trail, or a landscaping project. You’ll learn five practical methods using tools you likely already have: a phone, a tape measure, a level, a protractor, or a clinometer. By the end, you’ll be able to find the slope angle in degrees or percent, depending on what your project needs.

What You’ll Need

A smartphone with a built-in inclinometer (most modern phones have one in the Compass or Measure app) OR a clinometer (a handheld device for measuring slopes)
A tape measure (at least 10 ft / 3 m long)
A carpenter’s level (at least 2 ft / 60 cm long)
A protractor (for small slopes or when you don’t have a level)
A straight board or a long, straight piece of wood (optional, for leveling)
A pencil and paper to record measurements

Step-by-Step

Choose your method. Decide which tool you have on hand. The phone app is fastest; the level-and-tape method is most accurate for long slopes; the clinometer is best for outdoor terrain.
Method 1: Using a smartphone app. Open the Compass app (iPhone) or a level app (Android). Place the phone flat on the slope, with the top edge pointing uphill. Read the angle displayed. Most apps show degrees from 0 to 90. If your phone has a measure app, look for the “level” or “inclinometer” function.
Method 2: Using a level and tape measure. Place the level on the slope, with the bubble centered. Measure the vertical rise (in inches or cm) from the lower end of the level to the ground. Measure the horizontal run (the length of the level, e.g., 24 inches). Divide rise by run, then take the arctangent (tan⁻¹) of that number to get the angle in degrees. For example, if rise = 6 inches and run = 24 inches, rise/run = 0.25, and tan⁻¹(0.25) = 14.0°.
Method 3: Using a clinometer. Hold the clinometer to your eye, look through the sight, and aim at a point on the slope that is the same height as your eye (e.g., a spot on a tree or a building). Read the angle shown on the scale. This gives you the slope angle directly in degrees.
Method 4: Using a protractor and a plumb line. Tie a string to the center hole of a protractor, and tie a small weight (like a washer) to the other end. Hold the straight edge of the protractor parallel to the slope. The string will hang vertically; read the angle where the string crosses the protractor scale. That’s the slope angle.
Method 5: Using a laser level (for long slopes). Set up a laser level at the bottom of the slope. Mark a point on a pole at the top of the slope where the laser hits. Measure the vertical distance from the ground to that mark (rise) and the horizontal distance from the laser to the pole (run). Then use the same arctangent formula as in Method 2.
Convert to percent slope (if needed). Percent slope = (rise ÷ run) × 100. For example, a 14° angle has a percent slope of about 25% (since tan(14°) = 0.25).
Record your result. Write down the angle in degrees and the percent slope. Note whether it’s an uphill or downhill slope.

Common Mistakes

Confusing rise and run. Rise is vertical, run is horizontal. Mixing them up gives you the wrong angle.
Not holding the level perfectly horizontal. If the bubble isn’t centered, your rise measurement is off.
Using the phone on a curved surface. The app measures the angle of the phone’s back, so place it on a flat board if the slope is uneven.
Measuring from the wrong point. For a roof, measure the actual slope, not the ground underneath.
Forgetting to convert units. If you measure rise in inches and run in feet, convert one to the other before dividing.

Tips

For the most accurate results, take three measurements at different points along the slope and average them.
If the slope is very long, use a straight board to create a flat surface for your level or phone.
When using a clinometer, make sure your eye level is the same as the target point to avoid parallax error.
For a roof, measure the slope from the underside (the rafters) if possible, as shingles can add thickness.
Remember that a 45° angle equals a 100% slope—this is a handy reference.

Troubleshooting

Phone app gives wildly different readings each time. Calibrate your phone’s sensors by moving it in a figure-eight motion, or try a different app. Also, ensure the phone is flat against the slope.
Level won’t stay still on a steep slope. Use a longer board to spread the level out, or ask someone to hold it steady.
Protractor method is too imprecise. Switch to the level-and-tape method, which is more accurate for slopes under 30°.
You get a negative angle. That’s fine—it just means the slope is downhill. Take the absolute value for the steepness.
Your tape measure is too short. Use a longer tape or measure in segments, marking the end of each segment.

Frequently Asked Questions

What’s the difference between slope angle and percent slope?

Slope angle is measured in degrees (0° to 90°). Percent slope is the rise divided by the run, multiplied by 100. A 45° angle equals 100% slope. To convert from degrees to percent, use: percent = tan(angle) × 100.

Can I measure slope angle with just a tape measure?

Yes, if you have a level. Place the level on the slope, measure the rise over a known run (the level’s length), then use the arctangent formula. Without a level, you can’t get an accurate horizontal measurement.

What is a typical slope angle for a house roof?

Residential roofs typically have slopes between 20° and 35° (about 4/12 to 8/12 pitch). Low-slope roofs are under 10°, and steep roofs can be 45° or more. Local building codes often specify minimums for snow or rain.

How do I measure a slope angle on a hill outdoors?

Use a clinometer or a phone app. If you don’t have either, you can use a level and a long board: place the board on the hill, level it, then measure the rise at the lower end. The run is the length of the board.

Is a 30° slope steep?

Yes, 30° is considered steep. For reference, a 30° slope has a 58% grade, which is difficult to walk up and may require special equipment for vehicles. Most walking trails are under 10°.

Can I measure slope angle using a laser level?

Yes. Set the laser at the bottom, mark where it hits a pole at the top, measure the rise and run, then use the arctangent formula. This is a common method for long driveways or land grading.

Method: the standard formula for this calculation, rounded as each result states. See how the calculators work or report an error.