Last updated 10 September 2026
Quick answer: Open the free Roof Area & Panel Calculator, search your address, tap the corners of a roof section on the satellite photo and close the shape. It gives you the roof area in square metres, how many panels fit and the system size in kW. Add more sections if your roof has several usable faces.
Before an installer visits, it’s worth knowing roughly how big a system your roof can hold. A 6.6 kW system needs about 30 square metres of clear roof, a 10 kW system about 45, and a commercial 100 kW system somewhere near 500. You can measure your own roof from a satellite photo in a couple of minutes, and the numbers are good enough to sanity check any quote that lands in your inbox.
What is the Roof Area & Panel Calculator for?
It measures the area of any roof section you draw on satellite imagery, converts that flat plan area into the real sloped surface if you give it a tilt, then estimates how many panels fit and what that adds up to in kW. For Australian postcodes it also estimates yearly generation. The panel count is deliberately conservative: it assumes 75% of the drawn area is usable once you allow for edge setbacks, ridges, vents and aerials.
We covered the maths and the typical numbers in how many solar panels will fit on your roof. This post is about using the tool.
How do I use it?
Step one: search your address and let the map zoom in. Zoom in further if you can; the closer you are, the easier it is to hit the corners.
Step two: tap each corner of a roof section, going around in order. A line follows you from corner to corner. When you get back to where you started, tap near the first corner or hit Close this section, and the shape fills in. Made a mistake? Undo point removes the last corner.
Step three: repeat for any other roof face you’d consider putting panels on. Most homes have two or three worth measuring, usually the north, east and west faces. Skip the south face unless it’s the only option. The plan area shown is the total across all closed sections, with the section count next to it.
Step four: fill in the three fields under the map. Roof tilt converts your flat plan area into the actual sloped surface (a 22.5° roof has about 8% more surface than its footprint). Panel wattage defaults to 440 W, which is what most installers quote today; commercial jobs often use 550 W and up. And an Australian postcode adds a yearly kWh estimate using the same sun data as our Solar Panel Angle Calculator.
Drag any corner to fine tune the shape. The numbers update as you go.
How do I read the result?
The big number is the panel count. Next to it you get the plan area you drew, the sloped roof area after the tilt correction, and the system size in kW, with a note that 75% of the area is assumed usable. So a 60 square metre section at 22.5° with 440 W panels comes out to about 24 panels and 10.6 kW, and in Sydney that’s roughly 14,300 kWh a year if it’s well oriented.
Treat the panel count as a ceiling rather than a layout. A real design depends on panel orientation, rail runs and what’s actually on your roof, and that’s the installer’s job. What this tells you is whether the 10 kW system in a quote physically fits, or whether the 6.6 kW quote is leaving half the roof empty.
Can I measure a commercial roof?
Yes, and it’s arguably where the tool shines. Commercial roofs are big and simple to trace, so a warehouse takes four taps. For a flat roof set the tilt to 0 and keep in mind panels usually go on 10° to 15° frames with wider row spacing, so the real packing factor is lower than a pitched home roof. Knock the panel count back by a third and you’ll be in the right ballpark.
Does it store my roof outline?
No. There’s no database behind the tool. If you hit Copy link, the shape lives in the link itself, so only people you share it with can see it. Open the link on another device and the outline, tilt and postcode all come back.
Planning a system this size?
Once it’s on the roof, the question changes from how many panels fit to whether every one of them is working. A single faulty panel can drag down a whole string, and the inverter app usually won’t tell you. PV Fleet connects to the monitoring your inverter already has, learns what the system should produce and alerts you within hours when it doesn’t. Commercial starts at $790 per site per year and pays for itself by cutting maintenance spend and catching faults early. Book a free demo or see pricing.
All six free tools (roof azimuth, roof tilt, panel angle, roof area and panel count, a latitude and longitude finder, and a solar orientation comparison) are on the free solar tools page. No signup, and they work for any address.