Solar inverter size calculator
Size an inverter from your solar array — the recommended kW AC range, the DC/AC ratio and the nearest common size — or size an off-grid / hybrid inverter from your home's loads.
Quick answer: divide your array's kW DC by 1.35 to 1.1 — a 10 kW array wants a 7.4–9.1 kW inverter (a common 7.6 kW unit gives a DC/AC ratio of ~1.32). For off-grid, size the inverter ~25% above your heaviest load, with surge rating to match.
Mode A — from your solar array
Your array
Mode B — from your home loads (off-grid / hybrid)
Your loads
Ballpark, not gospel. Mode A follows the standard DC/AC rules installers use; Mode B is a sizing starting point for off-grid and hybrid systems. Real installs must respect the inverter's voltage windows, battery-charging limits and local electrical code — confirm with a licensed electrician before buying.
The rules this calculator uses
These are industry rules of thumb, applied exactly as the calculator does:
- Mode A — recommended range: array kW ÷ 1.35 (low end) to array kW ÷ 1.1 (high end). A DC/AC ratio around 1.1–1.35 is considered normal and economical — the inverter runs near its efficient range on sunny days while staying within its input limits.
- Mode A — nearest common size: the smallest of the standard sizes (3.0, 3.8, 5.0, 6.0, 7.6, 10.0, 11.4, 15.0 kW) at or above the low end of the range. Beyond the largest, the calculator says so: arrays over ~20 kW usually split across multiple inverters.
- Mode B — continuous rating: heaviest continuous load × 1.25, rounded up to the nearest 100 W. Surge rating: highest surge load × 1.25, rounded up the same way.
| Array (kW DC) | Inverter range (kW AC) | Common size | DC/AC ratio |
|---|---|---|---|
| 4 | 3.0–3.6 | 3.0 | 1.33 |
| 6 | 4.4–5.5 | 5.0 | 1.20 |
| 8 | 5.9–7.3 | 6.0 | 1.33 |
| 10 | 7.4–9.1 | 7.6 | 1.32 |
| 12 | 8.9–10.9 | 10.0 | 1.20 |
| 15 | 11.1–13.6 | 11.4 | 1.32 |
Table values computed with the same rules the calculator uses. On the guidance: a DC/AC ratio near 1.0 generally means paying for inverter capacity the array rarely fills; above ~1.4, clipping losses start to grow — most designs aim to sit in the 1.1–1.35 band.
Why inverter sizing matters
Too small: clipping
An undersized inverter clips — on bright days the array could produce more than the inverter's AC rating lets through, and the excess is lost. A little clipping is normal and economical (it's why installers deliberately target DC/AC ratios above 1.0); heavy clipping at ratios far past ~1.4 wastes real energy.
Too big: wasted money
An oversized inverter is safe but pointless: you pay for capacity the array can't fill, and it may run slightly less efficiently at low power. The one good reason to oversize is expansion — if panels will be added later, buy for the future array size, and check the inverter's DC voltage window suits the future string layout.
String vs micro vs hybrid
String inverters are the ones this calculator sizes. Microinverters skip the single-size decision entirely — one roughly 300–400 W unit sits behind each panel, so sizing is per-module. Hybrid (battery-ready) inverters size the same way as string inverters for the array, but must also handle battery-charging current and backup loads: read those specs carefully and get professional sizing for the backup side.
Questions people actually ask
Straight answers, no fluff. Then run your own numbers above.
What size inverter do I need for a 10 kW solar system?
A 10 kW DC array sits in a 7.4–9.1 kW AC inverter range. The nearest common size is 7.6 kW, giving a DC/AC ratio of about 1.32 — right in the normal, economical band. A 10.0 kW inverter also works but costs more for capacity the array rarely fills.
What is DC/AC ratio (inverter loading ratio)?
It's your array's DC wattage divided by the inverter's AC rating. Roughly 1.1–1.35 is considered normal and economical — the inverter runs near its efficient range on sunny days while staying within its input limits. Near 1.0 means paying for capacity the array rarely fills; above ~1.4, clipping losses start to grow.
What happens if my solar inverter is too small?
The inverter clips output at its rating — on bright days the array could produce more than the inverter lets through, and the excess is simply lost. A little clipping with a DC/AC ratio of 1.2–1.35 is normal and cheap insurance; heavy clipping at ratios far above ~1.4 wastes real energy. Check the inverter's maximum DC input rating and stay within it.
Is it bad to oversize a solar inverter?
It's safe but wasteful: a much larger inverter than the array needs costs more and can run slightly less efficiently at low power. An oversized inverter only makes sense if you plan to add panels later — then buy for the future array size, and check the inverter's minimum and maximum DC voltage window suits the future string layout.
How do I size an off-grid or hybrid inverter?
Size to your loads, not your panels: take the highest continuous load and multiply by about 1.25 for the inverter's continuous rating, and do the same for the highest surge load for its surge rating — that's what the calculator's off-grid mode does. Then have a licensed electrician size the wiring, disconnects and breakers for those ratings.
Do microinverters and hybrid inverters size differently?
Microinverters are sized per panel — one roughly 300–400 W microinverter behind each 400 W panel is typical, so there's no single 'inverter size' decision. Hybrid (battery-ready) inverters size the same way as standard string inverters for the array, but also need to handle battery charging current and backup loads — read the battery-charging specs, and get professional sizing for the backup side.
Sizing the full system around it? The solar system calculator sizes array and battery together, and the tilt angle calculator finds your best panel angle. For the deeper theory, read the solar inverters guide and the hybrid inverters guide.