Solar Inverter Sizing Calculator

SettingsSettings for this calculationUS

Market

Imperial · sales tax

Array DC rating (W)

Total nameplate DC watts of the panels.

Panel count times panel wattage at STC. This is the laboratory rating — an array almost never produces it in the field, which is exactly why the inverter is deliberately smaller.

DC to AC ratio

How much larger the array is than the inverter.

1.1 to 1.3 is standard. The array only reaches its DC rating in cold bright conditions for a few hours a year, so an inverter matched to the nameplate sits underused almost always. Over-sizing the array captures more energy in the many hours of partial output, at the cost of trimming a rare peak.

System losses (%)

Soiling, wiring, mismatch, temperature and inverter efficiency.

14% is NREL's default total derate for a well-installed system. Dusty, hot or partly-shaded sites run higher, and shading is the one that does not behave linearly — a single shaded cell can drag a whole string.

Inverter AC rating

5,000 W AC

Medium confidence

Capacity sizing only. String voltage limits, MPPT window, temperature coefficients and the local wiring rules all constrain the final selection.

Inverter rating: 5 kW AC
Array DC rating: 6 kW DC
Realistic peak AC after losses: 5.16 kW
Headroom over realistic peak: -3.1 %

Then change the inputs to see how far the answer moves.

Show calculation logic

How this was calculated

Formula source(s)

DC-to-AC ratio (ILR) of 1.1-1.3 is standard practice; NREL SAM documentation and inverter manufacturers' design guides
IEC 62109 and local wiring rules govern the electrical design; this sizes capacity only

Inputs used

Array DC rating (W): 6000
DC to AC ratio: 1.2
System losses (%): 14

Intermediate steps

Inverter rating: 5 kW AC
Array DC rating: 6 kW DC
Realistic peak AC after losses: 5.16 kW
Headroom over realistic peak: -3.1 %

Final result5,000 W AC

Confidence note: Capacity sizing only. String voltage limits, MPPT window, temperature coefficients and the local wiring rules all constrain the final selection.

What this calculation does not cover

Does not check string voltage against the inverter's MPPT window or its maximum input voltage — cold-weather open-circuit voltage is what breaks inverters and it depends on the panel's temperature coefficient.
Does not consider grid export limits, which in several markets cap the inverter rather than the array.
Shading is not modelled. Partial shading is better addressed with optimisers or microinverters than with sizing.

Add the equipment this sizes

This result is a specification — 5,000 W AC — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.

QtyItemPrice each ($)

Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.

Sources checked 2026-08-27 · in the site-wide review of 2026-09-06 · v1.0.0

Regulatory standards & verification citations2

DC-to-AC ratio (ILR) of 1.1-1.3 is standard practice; NREL SAM documentation and inverter manufacturers' design guides
IEC 62109 and local wiring rules govern the electrical design; this sizes capacity only

Cite this page

Your workspace

Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Now that you have the number

These guides cover the work this quantity is for — the first ones run this calculator inside the section that raises the question.

Getting Solar and a Battery Connected: Notification and Export Limitsuses this calculator

The network assesses what the inverter can push out, not what is on the roof — so the connection route has to be settled before the order goes in.

Siting a Home Battery: Garage, Utility, Loft or Outside Walluses this calculator

The position is settled at survey and it sets the separation, the cable run and the ambient the warranty is written against. Occasionally it ends the job.

Planning a Rooftop Solar Array

How to calculate solar inverter sizing in 4 steps

Array DC rating (W)Total nameplate DC watts of the panels.

DC to AC ratioHow much larger the array is than the inverter.

System losses (%)Soiling, wiring, mismatch, temperature and inverter efficiency.

Inverter AC ratingThe tool computes the inverter AC rating from those figures and shows the formula, its sources, and a confidence rating alongside it.

Array DC rating (W)	Inverter AC rating (W AC)
1,000	833
2,000	1,667
5,000	4,167
10,000	8,333
20,000	16,667
50,000	41,667

Array DC rating (W)

Inverter AC rating (W AC)

1,000

833

2,000

1,667

5,000

4,167

10,000

8,333

20,000

16,667

50,000

41,667

Frequently asked questions

Why is the inverter smaller than the array?

Because the array almost never produces its nameplate. Standard Test Conditions are 1000 W/m² at 25 °C cell temperature, which in the field happens for a handful of hours a year — panels run hot and lose output as they do. An inverter matched to the nameplate is idle capacity for the whole rest of the year, so the array is deliberately over-sized against it.

Does over-sizing waste energy?

A little, at the very top. When DC output exceeds the inverter's rating it clips, and that energy is lost. At a 1.2 ratio the clipping loss is typically well under 1% annually, against a much larger gain in the many partial-output hours. Above about 1.3 the trade starts running the other way.

What actually limits inverter choice?

String voltage more often than power. The array's open-circuit voltage rises as temperature falls, and the cold-morning figure must stay inside the inverter's maximum input — exceeding it damages the unit. Power sizing is the easy half of the problem; the voltage window is the half that needs the panel's temperature coefficient and your local record low.