DC-to-AC Power Conversion & Sizing
Inverter Size Calculator
Calculate the continuous and surge wattage needed to power your AC appliances from a 12V, 24V, or 48V battery bank, including DC current draw, fuse sizing, and cable gauge.
Size Inverter by Appliance Wattage
⚡ 1-Click Autofill: Top 5 Inverter Setups
How to Size an Off-Grid Inverter
- Sum Continuous Running Watts: Total the operating wattage of all AC appliances you intend to power simultaneously.
- Add Single Largest Motor Surge Delta: Motorized loads (compressors, pumps, power tools) require an extra startup burst of power.
- Add 20% Safety Headroom: Sizing with headroom prevents inverter overload alarms and heat throttling during sustained usage.
- Calculate DC Battery Cable & Fuse Amperage: Low-voltage DC cables carry massive amperage; always verify DC cable gauge (AWG) and Class-T fuse ratings.
Inverter Wattage, DC Current & Cable Sizing Matrix
DC amperage drawn from battery banks and recommended copper cable gauges (92% inverter efficiency):
| Inverter Rating | 12V DC Current | 24V DC Current | 48V DC Current | Recommended DC Fuse | Min Copper Cable |
|---|---|---|---|---|---|
| 500 Watts | 45.3 Amps | 22.6 Amps | 11.3 Amps | 60 Amp | 6 AWG (12V) / 10 AWG (48V) |
| 1,000 Watts | 90.6 Amps | 45.3 Amps | 22.6 Amps | 125 Amp | 2 AWG (12V) / 6 AWG (48V) |
| 2,000 Watts | 181.2 Amps | 90.6 Amps | 45.3 Amps | 250 Amp | 2/0 AWG (12V) / 4 AWG (48V) |
| 3,000 Watts | 271.7 Amps | 135.9 Amps | 67.9 Amps | 350 Amp | 4/0 AWG (12V) / 2 AWG (48V) |
| 5,000 Watts | — (Not practical) | 226.4 Amps | 113.2 Amps | 175 Amp (48V) | 2/0 AWG (48V) |
Inverter & DC Battery Current Sizing Formulas
Standard electrical engineering conversion from AC output demand to continuous DC battery current and peak motor surge ratings.
Formula
Continuous_Watts = Total_Load × 1.20 | DC_Amps = Continuous_Watts / (Battery_Volts × Inverter_Efficiency)Variable Definitions
Continuous_WattsRecommended Inverter Rating(Watts)- Continuous AC output rating with 20% safety headroom buffer
Surge_WattsPeak Inrush Surge Rating(Watts)- Continuous watts plus the single largest motor inductive startup delta
DC_AmpsDC Battery Current Draw(Amperes)- Maximum direct current drawn from battery bank cables under full load
Inverter_EfficiencyDC-to-AC Inversion Efficiency(%)- Internal conversion efficiency of the inverter (typically 90%–94%)
Engineering Notes & Standards
- Pure Sine Wave inverters are required for motorized equipment, digital electronics, and variable speed motors.
- DC fuses (Class-T or Mega/ANL) must be sized for 125% of maximum continuous DC current to prevent nuisance tripping.
Frequently Asked Questions (FAQ)
What size inverter do I need for my appliances?
Add the continuous wattage of all appliances you want to run simultaneously, then add 20% safety margin. If any appliance has an electric motor (refrigerator, blender, microwave, power tool), ensure the inverter's surge (peak) rating exceeds the startup inrush wattage of your largest device.
Why does a 12V inverter require thicker cables than a 48V inverter?
Power equals Voltage multiplied by Current (Watts = Volts × Amps). To deliver 2,000 Watts on a 12V system, the battery cables must carry approximately 185 Amps of DC current (requiring massive 2/0 or 4/0 AWG copper cable). On a 48V system, delivering the same 2,000 Watts requires only 46 Amps of current (requiring much thinner 6 AWG wire).
What is the difference between Pure Sine Wave and Modified Sine Wave inverters?
Pure Sine Wave inverters produce clean, smooth alternating current identical to (or cleaner than) grid utility power. Modified Sine Wave inverters produce choppy, stepped square-wave power that causes buzzing in motors, overheating in electronics, and failure in medical equipment (CPAP) or laser printers. Pure Sine Wave is strongly recommended for all modern setups.
What size DC fuse do I need for an inverter?
Size your DC fuse (Class-T or Mega/ANL) for 125% of the inverter's maximum continuous DC current. For example, a 1,000W inverter on a 12V battery draws about 93A DC at full load; multiplying by 1.25 gives 116A, so a 125A or 150A fuse is recommended.
Methodology and Standards
Inverter calculations use inductive motor starting characteristics and NEC 75°C copper ampacity standards. See our methodology and sources.
📜
Engineering Standards & Technical Methodology References
Calculations, electrical losses, and design safety margins adhere to recognized engineering guidelines:
NEC Article 706Energy Storage Systems (ESS)• National Electrical Code (NFPA 70)
Requirements for battery storage disconnects, circuit sizing, and ventilation in residential installations.
IEC 62619 / UL 1973Secondary Lithium Cells & Batteries Safety• IEC / Underwriters Laboratories
Safety requirements for industrial and residential lithium energy storage systems and BMS controls.
IEEE 1547-2018Standard for Interconnection & Interoperability• Institute of Electrical and Electronics Engineers
Grid-tie inverter synchronization, anti-islanding protection, and voltage/frequency ride-through.