Inclinometer.

Frequently asked questions.

What is grade percentage?

Grade (or gradient) expresses slope as the ratio of vertical rise to horizontal run, multiplied by 100 to give a percentage. A 10% grade means the terrain rises (or falls) 10 metres for every 100 metres of horizontal distance travelled. It is the standard unit used in road engineering, cycling, skiing, and civil construction because it communicates steepness in a way that is easy to apply practically. For reference: most paved roads stay below 10% grade; the steepest streets in San Francisco reach about 17%; the steepest public roads in the world (like Hardknott Pass in the UK) hit 33%; and avalanche-prone ski slopes are typically between 30–45%.

What is roof pitch?

Roof pitch is the standard way roofers, architects, and builders describe the steepness of a roof in the US and UK. It is written as rise-over-run where the run is always 12 inches — so a '6/12 pitch' means the roof rises 6 inches vertically for every 12 inches of horizontal distance, which equals an angle of about 26.6°. Low-slope roofs (2/12 to 4/12) are common on modern and commercial buildings. Standard residential roofs are typically 4/12 to 9/12. Steep roofs above 9/12 are found on older homes, barns, and steep-climate buildings designed to shed snow. This tool displays your measured angle automatically converted to X/12 format alongside the degree value.

How do I measure a roof with this tool?

Hold the long edge of your phone flat against the roof surface — or press it against a straight board placed on the roof for a more stable contact. The inclinometer immediately displays the slope angle in degrees and the equivalent X/12 pitch. The most important step is to tap Hold Reading before climbing down from the ladder or stepping back from the roof. This locks the displayed value so you can read it safely at ground level without the number changing as you move. If you need to measure multiple sections, take note of each, release the hold, reposition, and lock again.

What is the difference between an inclinometer and a spirit level?

A spirit level answers one specific question: is this surface perfectly horizontal (0° tilt)? It gives you a binary pass/fail — level or not level. An inclinometer measures the actual angle of any surface across its entire range, from 0° (flat) through 45° (1:1 slope) to 90° (vertical wall). You can think of the spirit level as a special case of the inclinometer focused exclusively on the 0° mark. Use the spirit level when you need to confirm flatness; use the inclinometer when you need to know the actual angle — measuring roof pitch, assessing trail grade, checking a ramp angle for accessibility compliance, or evaluating avalanche terrain.

How accurate is this measurement?

Consumer smartphone accelerometers are typically accurate to ±0.5–1° under normal conditions, which is adequate for the vast majority of practical uses — roofing, DIY construction, slope assessment, photography, and vehicle levelling. The main sources of inaccuracy are vibration (which introduces noise into the reading), sensor calibration drift (addressed by the calibration button), and holding the phone against an irregular surface (always use the longest, flattest edge of the phone for contact). For precision engineering, land surveying, or anything requiring accuracy better than 0.5°, a purpose-built hardware inclinometer with NIST-traceable calibration is recommended. For everyday tasks, the phone is more than sufficient.

Understanding Slope Measurement

An inclinometer — also called a clinometer, tilt meter, or slope meter — measures the angle of a surface relative to a perfectly horizontal plane. Our digital inclinometer uses your phone's accelerometer, the same sensor that detects rotation and tilt in video games and screen auto-rotation. Hold the edge of your phone flat against any surface and you instantly get the slope expressed four different ways: degrees, grade percentage, roof pitch, and rise/run ratio.

Degrees, grade, and pitch — what's the difference?

Degrees is the most intuitive unit: 0° is perfectly flat, 45° is a 1:1 slope, 90° is a vertical wall. It's the universal measure used in physics, trigonometry, and general reference.

Grade percentage is used in civil engineering, road construction, and cycling. It expresses rise as a percentage of horizontal run. A 10% grade means the elevation changes by 10 metres for every 100 metres of horizontal distance. A 100% grade is the same as a 45° angle. Professional cyclists consider anything above 15% very steep; Tour de France mountain stages regularly hit 20–24%.

Roof pitch is the standard unit in residential construction (especially in the US and UK). It is expressed as rise over a 12-inch horizontal run — a "6/12 pitch" means the roof rises 6 inches for every foot of horizontal distance, which equals about 26.6°. Most residential roofs fall between 4/12 and 9/12 pitch.

Rise/run ratio is common in accessibility standards, ramp design, and hiking trail descriptions. A 1:4 ratio means 1 unit of rise for every 4 units of run — a 25% grade or about 14°.

How to measure a roof with your phone

Hold the long edge of your phone flat against the roof surface (or against a straight board placed on the roof). The inclinometer will immediately display the angle. Use the Hold Reading button to lock the value before stepping off the ladder — this way you can read the pitch safely from the ground without the number changing. The tool shows the result in both degrees and the X/12 pitch format used by roofers, architects, and building supply stores.

Slope categories and what they mean

The tool classifies your measured angle into categories to give instant context:

• Flat (0–2°) — level ground, standard floors and roads.
• Gentle (2–10°) — easy walking paths, wheelchair-friendly ramps, most driveways.
• Moderate (10–20°) — steeper hiking trails, green ski runs, low-pitched roofs.
• Steep (20–35°) — challenging hiking, blue/red ski runs, typical residential roofs.
• Very steep (35–55°) — black diamond ski runs, aggressive off-road terrain, steep metal roofs.
• Extreme (55°+) — near-vertical faces, technical climbing terrain, double-black ski runs.

Practical applications

Construction and DIY: Check staircase angles (building codes typically require 30–37°), measure roof pitch before ordering materials, verify ramp compliance with accessibility regulations (the ADA recommends a maximum 1:12 ratio, which is about 4.8°).

Outdoor sports: Skiers and snowboarders assess avalanche risk by slope angle — avalanches most commonly release on slopes between 30° and 45°. Mountain bikers and trail runners gauge the difficulty of a descent. Paddlers measure riverbank angles to assess launch and exit points.

Photography and film: Camera operators use inclination to set precise Dutch angle tilts or to verify a camera is horizontal on uneven ground.

Vehicles and equipment: Check that a caravan or motorhome is within the safe operating angle for the refrigerator (typically within 3° of level). Verify a vehicle is on firm, safe ground before jacking it up.