Rex says
Everyday utility math — the kind you'd otherwise pull up four browser tabs for. I keep it to one clean answer.
Try a scenario
Click to load — tweak from there.Inputs
Result
DC:AC ratio
1.20
Continuous load fits? (1=yes)
1
Surge load fits? (1=yes)
1
Continuous power headroom
1,500
DC:AC ratio in normal range? (1=yes)
1
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How to use this
- 1Enter total continuous load (W).
- 2Enter largest motor surge watts (W).
- 3Enter candidate inverter continuous rating (W).
- 4Enter candidate inverter surge rating (W).
- 5Enter solar array size (if paired) (W).
- 6Read your dc:ac ratio on the right — it updates as you type.
- 7Hit Share to keep the scenario or send it to someone.
About this calculator
An inverter has to satisfy two separate ratings: continuous power (what it can sustain indefinitely) and surge power (a short burst, usually a few seconds, for motor startup). Undersizing either one causes nuisance shutdowns or failure to start equipment at all. This calculator checks your planned continuous load and largest motor surge against a candidate inverter's specs, and separately checks DC-to-AC sizing ratio if you're pairing the inverter with a solar array (a ratio of 1.1-1.3 DC:AC is normal and intentional, not an error, since panels rarely hit rated output simultaneously).
Worked example
Using the values the calculator loads with:
Inputs
- Total continuous load: 3500 W
- Largest motor surge watts: 4500 W
- Candidate inverter continuous rating: 5000 W
- Candidate inverter surge rating: 10000 W
- Solar array size (if paired): 6000 W
Results
- DC:AC ratio: 1.2
- Continuous load fits? (1=yes): 1
- Surge load fits? (1=yes): 1
- Continuous power headroom: 1,500
- DC:AC ratio in normal range? (1=yes): 1
What each field means
Inputs
- Total continuous load (W)
- The total continuous load used in the calculation, measured in W. Starts at 3500 W so you have a working example on load.
- Largest motor surge watts (W)
- The largest motor surge watts used in the calculation, measured in W. Starts at 4500 W so you have a working example on load.
- Candidate inverter continuous rating (W)
- The candidate inverter continuous rating used in the calculation, measured in W. Starts at 5000 W so you have a working example on load.
- Candidate inverter surge rating (W)
- The candidate inverter surge rating used in the calculation, measured in W. Starts at 10000 W so you have a working example on load.
- Solar array size (if paired) (W)
- The solar array size (if paired) used in the calculation, measured in W. Starts at 6000 W so you have a working example on load.
Results
- DC:AC ratio
- Returned as a decimal number and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Continuous load fits? (1=yes)
- Returned as a whole number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Surge load fits? (1=yes)
- Returned as a whole number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Continuous power headroom
- Returned as a whole number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- DC:AC ratio in normal range? (1=yes)
- Returned as a whole number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
Why would you intentionally oversize the DC array relative to the inverter?
Panels almost never produce their full rated output simultaneously except under ideal conditions (cool temps, perfect sun angle, clean panels), so a 1.1-1.3 DC:AC ratio 'clips' only a tiny amount of peak production on the best days while letting you use a smaller, cheaper inverter that's still adequately sized for real-world production the rest of the time.
What happens if the DC:AC ratio is too high?
Above roughly 1.35-1.4, you start losing meaningful production to clipping — the inverter simply can't pass through all the DC power the array is capable of producing at peak, wasting some of what you paid for in panels. Most designers cap the ratio around 1.25-1.30 as a sweet spot.
Does surge rating matter if I don't have well pumps or AC?
Less critical, but still relevant for a refrigerator compressor, a table saw, or any single device with a motor — even a 700W running-load fridge compressor can surge to 1,500-2,200W for under a second at startup, and an inverter that can't cover that will trip or fail to start the load at all.
How is inverter sizing different for grid-tied vs off-grid?
Grid-tied inverters mainly need to handle the DC:AC array ratio correctly since the grid absorbs any load imbalance; off-grid and battery-backup inverters additionally need to cover 100% of your home's actual load and surge requirements on their own, since there's no grid to lean on if the inverter is undersized.
Accuracy and limitations
- Estimates assume standard, average conditions — local rules, pricing, and materials vary.
- Results are rounded for readability; add a buffer before ordering, booking, or committing.
- Double-check anything with a real cost attached against a local quote.
Related tools
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). Inverter Sizing Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/inverter-sizing
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/inverter-sizing" target="_blank" rel="noopener">Inverter Sizing Calculator — RevenueLab</a> (2026).</p>
Source: [Inverter Sizing Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/inverter-sizing) (2026).