System sizing, 60 tools

How many panels do you actually need?

Start from your monthly bill, your square footage, or your roof's own geometry. These tools handle the math for panel count, layout, tilt, and the space you actually have to work with.

Start here

The tool most people run first

Solar panel calculator Panel count from your monthly usage. The starting point for every other tool on this page.

Sizing is only half the question. Once you have a panel count, the annual kWh output estimator shows what that system actually produces in a year, and the payback period calculator turns that output into a savings timeline. The US Department of Energy's homeowner's guide to going solar covers the same decisions in plain language, and NLR's PVWatts calculator lets you check any estimate against modeled output for your exact address.

By starting point

Size from what you already know

Solar panel calculator System size by monthly kWh usage System size by annual kWh usage System size by household size System size by square footage, quick estimator System size by electric bill amount Quick 5-minute system size estimator kW to panel count converter

By home size

Size for a specific square footage

System size for a 1,500 sq ft home System size for a 2,000 sq ft home System size for a 2,500 sq ft home System size for a 3,000 sq ft home

Roof and layout

Fit the array to the roof you have

Roof space vs output estimator Usable roof area calculator Panel spacing and setback calculator Fire code setback loss calculator Roof pitch output adjustment calculator Roof azimuth orientation calculator Array tilt angle optimizer Multi-roof plane array splitter Irregular roof shape array fitter Dormer and obstruction loss calculator Tree line setback sizing tool Ground mount vs roof mount space calculator South-facing vs east-west array calculator Seasonal tilt adjustment calculator Carport solar sizing calculator Pergola solar sizing calculator Partial roof shading sizing adjustment Chimney and vent obstruction loss calculator Skylight obstruction loss calculator Compact roof high-density layout tool Maximum roof capacity calculator Array weight load per panel calculator

Planning ahead

Sizing for future additions

Oversizing for a future EV Oversizing for a future battery Panel count for a net-zero home Panel count for 100% offset Panel count for 90% offset Panel count for 110% offset Panel count rounding tool Minimum viable system size calculator System size for a net metering cap limit

Panels and wattage

Compare panel choices before you commit

Panel wattage vs count tradeoff tool Panel count to kW converter Panel efficiency vs space tradeoff tool High efficiency vs standard panel count comparison Bifacial panel output addon calculator System size comparison by panel brand and wattage

Electrical and equipment

Sizing the wiring behind the panels

DC to AC ratio calculator Inverter clipping threshold calculator String length vs panel count calculator

Specific loads and additions

Sizing around a particular appliance or building

System size for an all-electric home System size for a gas-to-electric conversion System size for a heat pump addition System size for an electric water heater addition System size for a pool heating addon System size for a hot tub addon System size for a workshop addon System size for a detached garage

Questions

Frequently asked

It depends mainly on your electricity usage and your local peak sun hours. The solar panel calculator converts your monthly usage into a panel count directly, and the square footage estimator gives a rough number if you don't have a recent bill handy.

Yes. Setbacks, vents, chimneys, and irregular roof shapes all reduce usable area below your roof's total square footage. The usable roof area calculator and obstruction loss calculator account for this directly.

If you're planning an EV or a battery within the next few years, it's usually cheaper to oversize now than to add a second array later. See the EV oversizing tool and battery oversizing tool.

An east-west layout produces a flatter output curve across the day rather than a single midday peak, and total output is somewhat lower than true south. The roof azimuth calculator shows the difference for your specific roof.