Inverter Sizing & DC Current Sizer
IEEE 929 & UL 1741 REFERENCE METHODOLOGYDetermine required continuous AC rating, peak surge capability, and DC input current from your battery bank — with continuous and surge loads strictly separated.
How inverter sizing works
An inverter converts DC battery power to AC for your loads. Sizing it is really two separate questions kept strictly apart: continuous power (what the inverter must supply indefinitely) and surge / peak power (the brief, higher draw when motors or compressors start).
Formulas
The inverter sizing math
Continuous watts, peak surge, and DC terminal current.
P_continuous = Σ load continuous watts
Steady-state power. Inverter continuous rating must exceed this value.
I_DC = P_AC ÷ (V_system × η)
Current drawn through DC battery cabling and main system fuse.
Frequently asked questions
How do I size an inverter?
Add up the continuous watts of everything the inverter must run for the minimum continuous rating. Then add the total surge power on top of the continuous figure to find the peak rating required. Choose an inverter whose continuous and surge ratings each meet or exceed those figures.
What size inverter do I need for 2000 watts?
If 2000 W is your continuous load, the minimum continuous rating is 2000 W. The surge requirement depends on your startup spikes: a 2200 W continuous plus 800 W surge needs a 3000 W peak capability.
How do I calculate the battery current an inverter draws?
Divide the AC output watts by the battery voltage times the inverter efficiency. At 90% efficiency on a 24 V system, 600 W of AC output draws 600 ÷ (24 × 0.9) = about 27.8 A from the battery.
What is the difference between continuous and surge inverter power?
Continuous power is what the inverter can supply indefinitely. Surge (peak) power is the higher, brief output needed for motor or compressor startup, typically handled for seconds. Both must be sized.
Related Calculators
Continue your system design with the other tools in the SolarCalcKit suite — in the order the rest of your design flows: load audit → battery → bank wiring → MPPT → wire size → inverter.
Solar Load Calculator
Start by auditing daily appliance energy use (Wh & kWh) and connected load.
Open ToolSolar Battery Calculator
Size a battery bank from that daily energy, autonomy days, chemistry and depth of discharge.
Open ToolBattery Bank Wiring
Turn a target kWh or Ah into an exact series–parallel battery configuration.
Open ToolMPPT Charge Controller
Size the charge controller from PV array wattage and the battery system voltage.
Open ToolSolar Wire Size / Drop
Size DC conductors from current, run length and allowable voltage drop.
Open Tool