Solar Panel Angle Calculator: Best Tilt and Roof Pitch in Degrees

A solar panel angle calculator gives a fixed tilt close to your latitude for the most yearly output, plus seasonal angles, and converts your roof pitch to degrees. With the defaults, latitude 37°N gives a year-round tilt of 37°, and a 5/12 roof is 22.6°, close enough that flush mounting usually makes sense.

How to use the solar panel angle calculator

1. Your state. Fills the Latitude of a major city in that state.
2. Latitude. Your home's latitude in degrees north. Any map app shows it. Default 37°N, roughly the middle of the continental US.
3. Roof pitch (rise per 12 in. run). A "5/12" roof rises 5 inches for every 12 inches across. Enter 5. Default 5.

You get four angles: Best fixed year-round tilt, Your roof angle, Summer-favoring tilt and Winter-favoring tilt, shown side by side in a bar chart. A schedule converts common pitches (2/12 through 12/12) to degrees and shows how far each is from your year-round tilt. This tool has no scenario table, since the pitch schedule already compares the options.

How the calculation works

Year-round tilt  = latitude
Summer tilt      = latitude − 15° (not below 0°)
Winter tilt      = latitude + 15° (not above 90°)
Roof angle       = arctan(rise ÷ 12) in degrees
Difference       = roof angle − year-round tilt

The year-round figure is a widely used rule of thumb for fixed, south-facing panels, not a site-specific optimum. Local weather, such as cloudy seasons or haze, can shift the true best angle at a given site. The tool calls your roof "close enough" when the difference is 15 degrees or less, a practical threshold rather than a code or efficiency standard. For a precise answer, run PVWatts (opens in a new tab) at several tilts for your address.

Worked example

Default inputs: latitude 37°N, roof pitch 5/12.

• Best fixed year-round tilt: 37°.
• Your roof angle: arctan(5 ÷ 12) = 22.6°, 14.4° below the year-round tilt.
• Summer-favoring tilt: 22°; winter-favoring tilt: 52°.
• Because the roof is within 15°, flush mounting usually makes sense, and 22.6° sits inside DOE's 15 to 40 degree range.

Second example, a low-slope roof in Phoenix: latitude 33.4°N, roof pitch 3/12.

• Year-round tilt: 33.4°; summer: 18.4°; winter: 48.4°.
• Roof angle: 14.0°, 19.4° below the year-round tilt.
• The tool suggests asking for a production estimate at your actual pitch. In Phoenix's strong sun, a 14° roof can still produce well, but the estimate should reflect it. Our guide to solar panels in Arizona covers local factors.

Roof pitch to degrees (vs a 37° year-round tilt)

What your result means

For most pitched roofs, the answer is "mount flush and check the production estimate." DOE notes that south-facing roofs sloped 15 to 40 degrees generally perform best (DOE (opens in a new tab)), which covers pitches from about 3/12 to 10/12.

If your roof is outside that range, do not rule solar out. Ask each installer for a production estimate at your real pitch and direction, and compare the kWh per kW figure across quotes. A bid that shows the same output for a 2/12 roof and a 7/12 roof has probably not modeled your house. For ground mounts or flat roofs, where you choose the angle, the year-round tilt is a reasonable starting point to test in PVWatts.

Tilt affects output, which affects savings. Turn your roof angle into kWh with the solar panel output calculator or PVWatts, then check how many panels fit with the roof calculator. Our guide on whether solar panels are worth it shows how output feeds into payback.

Rules that change the answer

• Orientation. Tilt advice assumes panels face true south. East- and west-facing panels do better at lower tilts.
• Tilt racks and codes. Tilting panels above the roof plane raises wind loads and may need engineering. Some local codes also limit how far panels may sit above the roof or near the ridge (Spokane County example (opens in a new tab)).
• Time-of-use and net billing. Where exports are valued by hour, such as California's Net Billing Tariff, west-facing panels that produce more in late afternoon can be worth more than their kWh suggest.
• Snow. Steeper tilts shed snow faster in northern states.

Common mistakes

• Treating latitude tilt as a must-have rather than a rule of thumb.
• Reading "5/12" as 5 degrees instead of about 22.6°.
• Paying for tilt racks on a pitched roof for a small gain.
• Ignoring azimuth: a steep north-facing roof is a poor site at any tilt.
• Forgetting row shading when tilting panels up on a flat roof.

Limits of this calculator

This is an educational rule-of-thumb tool, not a production model. It does not account for local weather, azimuth, shading or time-of-use value. Use PVWatts or your installer's production report for site-specific output at your real tilt and direction.