How many solar panels fit on my roof?
Far more than you need. Across the 788 cities we have measured, the median roof could physically hold about 63 panels — while a typical home only needs 15 to 22. Roof capacity is rarely the limit. Shading, orientation and how much electricity you actually use are.
The number nobody publishes
"How many panels fit" and "how many panels do I need" get treated as the same question. They are not, and the gap between them is enormous. Using Google's aerial imagery across 788 cities, the median rooftop measures about 193 m² and could take roughly 63 panels. The median home needs closer to 17.
The arithmetic
A standard 400W residential panel is roughly 1.87 m × 1.13 m — about 2.1 m² (22.5 sq ft) each. So in theory:
| Usable roof area | Panels that fit | System size |
|---|---|---|
| 20 m² (215 sq ft) | 9 | 3.6 kW |
| 40 m² (430 sq ft) | 19 | 7.6 kW |
| 60 m² (646 sq ft) | 28 | 11.2 kW |
| 80 m² (861 sq ft) | 38 | 15.2 kW |
| 120 m² (1291 sq ft) | 57 | 22.8 kW |
The catch is the word usable. Your total roof area and your usable area are very different numbers.
What eats your usable area
- Fire code setbacks. The one people never expect. Most jurisdictions require clear pathways — commonly 3 ft along ridges and sometimes along edges — so firefighters can move. On a small or complex roof this can remove a third of the surface before anything else.
- Obstructions. Plumbing vents, chimneys, skylights, dormers, satellite dishes. Each needs clearance, not just its own footprint.
- Wrong-facing planes. In the northern hemisphere a north-facing slope produces 30-50% less and is rarely worth using. Orientation compared →
- Shading. Area that is shaded for much of the day is area you should not fill. This is usually the real constraint, and the hardest to judge from the ground. How to assess it →
Worked example
A 1,600 sq ft roof (about 149 m²) with two slopes:
- North-facing slope unusable → 75 m² left
- Fire setbacks take roughly 25% → 56 m² left
- Two vents and a chimney with clearance, about 8 m² → 48 m² left
- 48 ÷ 2.1 ≈ 22 panels, roughly 8.8 kW
Total roof 149 m²; usable 48 m². Most of a roof is not panel space, which is why estimating from floor area or a satellite screenshot goes wrong.
Capacity by city
Measured median roof size and panel capacity, from Google's imagery:
| City | Median roof | Panels that fit | Panels typically needed |
|---|---|---|---|
| Phoenix, AZ | 215 m² | 78 | 17 |
| Houston, TX | 280 m² | 80 | 20 |
| Chicago, IL | 331 m² | 95 | 22 |
| Atlanta, GA | 308 m² | 83 | 21 |
| Denver, CO | 135 m² | 45 | 19 |
| Toronto, ON | 112 m² | 19 | 24 |
The right-hand column is the one that matters. Filling the left-hand column costs far more and returns less, because you cannot save money on electricity you were never going to buy. Why exports pay so little →
Getting your actual number
Estimating from floor plans or eyeballing a satellite photo will not account for setbacks, obstructions or shading. Enter your address and we read your specific building from Google's aerial and 3D imagery — usable area, panel count and measured sunlight hours after shading, for your roof rather than an average one.
What this looks like in real cities
Measured rooftop data, spanning the range from fastest to slowest payback we have found:
| City | Sun hrs/yr | Rate | Payback |
|---|---|---|---|
| Kahului, HI | 1,627 | 42.1¢ | 3.5 yrs |
| Marquette, MI | 1,426 | 19.1¢ | 8.8 yrs |
| Norman, OK | 1,781 | 12.1¢ | 11 yrs |
| Layton, UT | 1,665 | 11.2¢ | 13 yrs |
| Trois-Rivières, QC | 1,347 | 7.9¢ | 31.9 yrs |
Frequently asked
How much roof space does one solar panel need?
About 21 sq ft, or roughly 2 square metres, for a standard 400W residential panel. Real installations need more than the panel area alone: setbacks from roof edges, clearance around vents, and access paths all reduce what you can actually use, usually by a meaningful margin.
Can my roof fit enough panels to power my whole house?
For most homes, comfortably yes. A typical roof holds far more panels than an average household's usage requires, so consumption usually runs out before roof space does. The tight cases are small footprints, heavily shaded roofs, or homes with unusually high use from electric heating or EV charging.
Should I fill my whole roof with panels?
Usually not. Once a system covers your annual usage, extra panels mostly generate exports, credited at a lower rate than the retail power they replace. That means payback stops improving and eventually gets worse. Size to your usage, plus headroom for an EV or heat pump later.
Related guides
General information, updated 2026-08-22. Not financial, tax or engineering advice.