Reference
Degrees, percent grade, roof pitch, and solar tilt — the numbers this tool's readout maps to, worked out so you don't have to do the trig yourself.
Table 1
This tool reads in degrees. Contractors often think in roof pitch (rise per 12" of run); drainage and ramp specs are usually in percent grade. Here's how the same slope reads in each.
| Degrees | Percent grade | Roof pitch (X/12) | Slope ratio |
|---|---|---|---|
| 0.0° | 0.0% | 0/12 (flat) | — |
| 1.0° | 1.7% | 0.21/12 | 1 : 57.3 |
| 2.0° | 3.5% | 0.42/12 | 1 : 28.6 |
| 3.0° | 5.2% | 0.63/12 | 1 : 19.1 |
| 4.8° | 8.3% | 1/12 | 1 : 12.0 |
| 5.0° | 8.7% | 1.05/12 | 1 : 11.4 |
| 7.0° | 12.3% | 1.47/12 | 1 : 8.1 |
| 9.5° | 16.7% | 2/12 | 1 : 6.0 |
| 10.0° | 17.6% | 2.12/12 | 1 : 5.7 |
| 14.0° | 25.0% | 3/12 | 1 : 4.0 |
| 18.4° | 33.3% | 4/12 | 1 : 3.0 |
| 22.6° | 41.7% | 5/12 | 1 : 2.4 |
| 26.6° | 50.0% | 6/12 — common residential pitch | 1 : 2.0 |
| 30.3° | 58.3% | 7/12 | 1 : 1.7 |
| 33.7° | 66.7% | 8/12 — steep pitch | 1 : 1.5 |
| 36.9° | 75.0% | 9/12 | 1 : 1.3 |
| 39.8° | 83.3% | 10/12 | 1 : 1.2 |
| 45.0° | 100.0% | 12/12 — 45° A-frame | 1 : 1.0 |
Calculated directly: percent grade = tan(angle) × 100; roof pitch = tan(angle) × 12. Highlighted rows are the whole-number pitches (1/12 – 12/12) builders actually order material against.
Table 2
For a fixed (non-tracking) array, the standard rule of thumb is tilt ≈ your latitude, which balances summer and winter sun position for the best annual output. Some engineering guidance biases this slightly flatter (roughly 0.85–0.9× latitude) to favor summer's longer, clearer days — the difference is usually inside the ±10° window where yield loss is under 2%.
| Latitude | Example city | Fixed year-round tilt | Winter tilt (lat. + 15°) | Summer tilt (lat. − 15°) |
|---|---|---|---|---|
| 10°N | San José, Costa Rica | 10° | 25° | 0°* |
| 19°N | Mexico City, MX | 19° | 34° | 4° |
| 26°N | Miami, FL | 26° | 41° | 11° |
| 30°N | Houston, TX | 30° | 45° | 15° |
| 34°N | Los Angeles, CA | 34° | 49° | 19° |
| 38°N | San Francisco / Denver | 38° | 53° | 23° |
| 40°N | New York, NY / Madrid | 40° | 55° | 25° |
| 42°N | Boston, MA / Rome | 42° | 57° | 27° |
| 45°N | Portland, OR / Milan | 45° | 60° | 30° |
| 48°N | Seattle, WA / Paris | 48° | 63° | 33° |
| 51°N | London, UK | 51° | 66° | 36° |
| 52°N | Berlin, DE | 52° | 67° | 37° |
| 55°N | Moscow, RU / Copenhagen | 55° | 70°* | 40° |
*Winter/summer tilts are capped near practical mounting limits; extreme values are rarely worth the added wind load. Southern Hemisphere: use the same latitude value but face panels true north instead of true south.
Reference
Quick definitions for the axis labels on the gauge and the units in the tables above.
The forward/backward tilt of the device — nose up or nose down. On this tool, pitch is what changes when you lift one end of the phone while it lies on a surface.
The side-to-side tilt — left edge up or right edge up. Roll and pitch together describe the full tilt of a flat surface.
Rotation around the vertical axis — compass heading, not tilt. This tool doesn't measure yaw, since it has no bearing on whether a surface is level.
Rise divided by run, ×100. A 10% grade rises 10 units for every 100 units traveled horizontally. Common in road, ramp, and drainage specs.
Rise per 12 inches of horizontal run, written X/12. A "6/12" roof rises 6 inches for every 12 inches inward — that's 26.6°.
Setting the current tilt reading as the new 0° reference, so all further readings are measured relative to that surface instead of true level.
Open the tool, place your phone on the surface, and match it against the table above.
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