How to Measure Your Roof for Solar Panels

Thinking about going solar? The first thing any installer will ask is how much usable roof space you have. You can figure that out yourself in five minutes with a satellite map. No ladder, no tape measure, no appointment.

This guide walks you through measuring your roof with Area Sketcher's Google Maps calculator, estimating how many panels will fit, sizing a system in kilowatts, and understanding whether battery storage like a Tesla Powerwall makes sense for your home.

Solar roof calculator

Enter your roof measurements below to instantly see how many panels fit, your system size, estimated annual production, and recommended Powerwall count. The guide below explains how to get each number.

How to measure your roof

Step 1: Find your roof on satellite view

Open the Google Maps area calculator and search for your address. The map will jump to your location on satellite imagery.

Zoom in until your roof fills most of the screen. You want to clearly see the edges of the roof, including ridgelines, hips, and any obstructions like chimneys or dormers.

Tip: Satellite images are taken from slightly off-center, which means the roof outline you see is a projection. For most residential roofs with moderate pitch, this introduces less than 5% error. For steep roofs, the calculator above corrects for pitch automatically.

Step 2: Measure total roof area

Select the Area tool and click points around the perimeter of your entire roof. Follow the edges as closely as possible. When you close the polygon by clicking the first point, the area appears instantly.

Name this measurement "Total Roof" in the side panel.

If your roof has multiple sections at different heights or angles (common with L-shaped or T-shaped homes), measure each section as a separate polygon. The side panel will show individual areas and a running total.

Step 3: Subtract unusable space

Not every square foot of roof is usable for solar. You need to subtract:

• Chimneys and vents: draw small polygons around each one
• Skylights: measure and subtract
• HVAC equipment: rooftop units need clearance around them
• Dormers: the face of a dormer is usually too small and poorly oriented
• Setbacks: most building codes require panels to be at least 18 inches from roof edges and ridgelines for fire access
• Shade zones: areas shaded by trees, neighboring buildings, or other parts of your own roof for significant portions of the day

Draw a polygon around each obstruction, name it (e.g. "Chimney", "Vent setback"), and note the area. Subtract these from your total and enter both numbers in the calculator above.

Example:

• Total roof: 1,800 sq ft
• Chimney + vents: 25 sq ft
• Edge setbacks (18 in on all sides): ~280 sq ft
• North-facing section: 450 sq ft
• Unusable area: 755 sq ft

Understanding the results

Panels and system size

The calculator corrects for roof pitch (a sloped roof has more surface area than its footprint), then divides by the panel size for your chosen brand. It reduces the count by 15% for spacing, wiring, and racking hardware.

Standard residential panels range from 350-430W. The difference between brands is small. What matters most is how much usable roof area you have.

Annual production

Production depends on your region's sunlight hours. The calculator gives a range based on typical values for your area. The average US household uses about 10,500 kWh per year. If production exceeds that, you'd either install fewer panels or use the extra to offset electric vehicles, pool heaters, or other large loads.

Tesla Powerwall

A Tesla Powerwall is a home battery that stores solar energy for use at night or during outages. Each Powerwall 3 stores 13.5 kWh of usable energy and includes a built-in solar inverter that handles up to 11.5 kW of solar input.

You likely need a battery if:

• You want backup power: even a large solar system shuts off during grid outages for safety. A Powerwall keeps your lights on.
• Your utility uses time-of-use rates: store cheap solar energy during the day and use it during expensive evening peak hours.
• You don't have net metering: if your utility doesn't credit you fairly for exported solar energy, storing it is more valuable than sending it to the grid.

Enter your daily energy usage in the calculator to see a recommendation. Your daily usage is on your electricity bill. The US average is about 29 kWh/day.

You don't need to decide on batteries right now. Most solar systems can be retrofitted with a Powerwall later. But knowing your roof area and system size helps you plan ahead.

Orientation and tilt matter

Not all roof faces produce equally. In the Northern Hemisphere:

• South-facing: optimal, receives the most annual sunlight (100% production)
• Southwest or Southeast: very good, about 85-95% of south-facing production
• West or East: decent, about 75-85% of south-facing production
• North-facing: poor, typically 50-65%. Usually not worth installing panels on

When measuring your roof, note which sections face which direction. Focus your panel count on south, southwest, and southeast sections first.

You can check orientation directly in the Area Sketcher map tool. The compass on the map shows north, and you can compare your roof edges to cardinal directions.

What to bring to your installer

After measuring with Area Sketcher, you'll have everything an installer needs for an initial assessment:

1. Total roof area and usable area after subtracting obstructions and setbacks
2. Roof orientation: which sections face south, east, west
3. Approximate panel count and system size in kW
4. Your annual electricity usage from your utility bill (usually listed as kWh/year)

This puts you in a much stronger position during consultations. You'll be able to compare quotes intelligently and catch any installer that's over- or under-sizing your system.

Start measuring

Open the Google Maps area calculator, search for your address, and trace your roof. In five minutes you'll know exactly how much solar your roof can support.