How many solar panels fit on my roof?

Divide your usable roof area (after setbacks) by panel dimensions. A 30 by 20 foot roof section with 3-foot setbacks fits about 16 typical 400-watt panels. Use the estimator above with your measurements.

What is the setback requirement for solar panels?

Many jurisdictions following the International Residential Code require 3-foot clear paths along roof edges and ridges for firefighter access. Rules vary — confirm with your local building department and installer.

Should panels be portrait or landscape?

Whichever fits more panels on your roof section. Portrait usually wins on wide roofs, landscape on tall narrow ones. The estimator above tries both and shows the better fit.

Solar Panel Roof Layout Estimator — How Many Panels Fit?

Fit check

Roof section length (ft)

Roof section width (ft)

Panel length (in)

Typical 400W panel ≈ 65" × 39". Check your panel spec sheet.

Panel width (in)

Edge setback (ft)

3 ft is common under IRC fire-access rules; your jurisdiction may differ.

Panel wattage (W)

Before you count on this: vents, chimneys, skylights, dormers, and racking rails eat real roof. Fire setbacks vary by jurisdiction. An installer does a shade and structural survey — this page just tells you whether the section is in the right ballpark.

Frequently asked

Do panels have to face south?

South-facing is best in the Northern Hemisphere, but east/west roofs still produce well (roughly 80–85% of south). North-facing sections are usually skipped. Azimuth matters less than avoiding shade.

How much does a panel weigh?

A typical residential panel weighs 40–50 lbs, spread over its mounting points. Most modern roofs handle this fine, but older roofs may need a structural check — your installer confirms this.

How this estimate works

The estimator shrinks your roof section by the setback on all four sides, then tiles panels across the remaining rectangle twice — once in portrait (tall side up), once in landscape — and reports whichever orientation fits more panels. Panel dimensions default to a typical modern residential panel, about 65 by 39 inches at 400 watts, but panels vary by model, so measure against the spec sheet of the panel you are actually quoted. The result is a count for one clear rectangular section. Real roofs are chopped up by vents, chimneys, skylights, and dormers, and installers also leave working room around obstructions, so treat the number here as a ceiling for that section, not a promise. If two orientations tie, portrait is usually cheaper to rack on a wide roof because the rails run shorter spans.

Examples

Standard gable section, 30 × 20 ft. With 3-foot setbacks the usable area is 24 × 14 ft. Portrait panels (about 5.4 ft tall) stack two rows of twelve: 16 to 24 panels depending on exact panel width — the estimator's answer for typical 400W panels is 16, about 6.4 kW from this one section. That is a full system for many homes, from a single clean roof face.

Small section, 18 × 12 ft. Setbacks leave 12 × 6 ft. One row of portrait panels fits — roughly 6 panels, 2.4 kW. Sections this size are usually combined with a second face rather than used alone, and installers may skip a face this small if the racking cost per panel gets silly.

Long ranch section, 44 × 16 ft. Usable 38 × 10 ft fits two portrait rows of about 19, or roughly 28 to 38 panels across orientations — more than most homes need, which is the good problem: the constraint becomes your electrical panel and usage, not your roof.