Solar Inverter Size Calculator
Pick an inverter size for a grid-tied array, or for an off-grid or backup system.
There are two ways to size an inverter. A grid-tied system sizes it from the solar array. An off-grid or backup system sizes it from the loads it has to run, including the moment a motor starts.
Pick the system type at the top of the calculator. The fields change to match.
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Planning estimates only. Your roof, equipment, utility rules and weather change the real numbers, so get a written quote before you buy. Data as of October 2026.
How this calculator works
Grid-tied
The inverter’s AC rating is the array’s DC rating divided by the DC to AC ratio. A ratio around 1.2 is common, so a 9.6 kW array pairs with an 8 kW inverter. Panels rarely put out their full rated power, because of heat, sun angle and dirt, so the inverter seldom runs at its limit. The small amount it clips at midday costs only a little of the yearly energy.
The tool lists the common inverter sizes around your array with the ratio each one gives, so you can see where clipping starts.
Off-grid or backup
The tool takes your peak running load, adds a safety margin (25% by default) and picks the next standard size up. It then checks the surge: most inverters can supply about twice their rating for a few seconds. It also shows the current on the battery side at full load, which you need for cable and fuse sizes.
Microinverters
A microinverter sits under each panel. Add up their ratings to get the total AC size. A 400 W panel usually pairs with a micro rated about 300 to 370 W.
Questions
What size inverter do I need for an 8 kW solar system?
At a ratio of 1.2, about 6.7 kW AC. The closest common sizes are 6 kW and 7.6 kW. Many installers pick 7.6 kW so the inverter never limits the array.
Can the inverter be smaller than the solar array?
Yes, and it usually is. A DC to AC ratio of 1.1 to 1.3 is normal. You pay for less inverter and lose very little energy.
What happens if the inverter is too small?
It clips. When the panels make more than the inverter can handle, the extra is lost. That happens for a few hours around noon on the best days, so a mild amount is fine and a large amount isn’t.
String inverter or microinverters?
A string inverter is cheaper and works well on a simple, unshaded roof. Microinverters or optimizers earn their price when parts of the roof are shaded or face different ways.
How long do inverters last?
A string inverter often needs replacing after 10 to 15 years, before the panels wear out. Warranties run from about 10 to 12 years for string models to 25 years for many microinverters.
What inverter do I need for an off-grid cabin?
Add up what runs at once, add 25%, and check the surge for pumps and other motors. The tool does the sums. Above about 3,000 W, use a 48 V battery.
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