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 continuous DC current draw, illustrative fuse sizing, and cable gauge guidance.
Size Inverter by Appliance Wattage
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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: Startup current varies by equipment. If available, use the manufacturer's specified starting/inrush requirement or measured startup load. A 3×–5× multiplier is only a rough planning example.
- Add 20% Illustrative Planning Headroom: Sizing with headroom prevents inverter overload alarms and heat throttling during sustained usage. Actual inverter selection should consider manufacturer ratings, continuous-load requirements, environmental conditions, and expected load variability.
- Calculate DC Battery Conductor & Fuse Sizing: Low-voltage DC cables carry substantial amperage; always verify DC conductor sizing and fuse ratings against manufacturer specifications and applicable electrical codes.
Inverter Wattage, DC Current & Cable Sizing Matrix
DC amperage drawn from battery banks and illustrative copper cable gauges (based on 92% inverter efficiency):
| Inverter Rating | 12V DC Current | 24V DC Current | 48V DC Current | Illustrative Fuse Size | Illustrative Cable Size |
|---|---|---|---|---|---|
| 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 | 300 Amp (24V) / 175 Amp (48V) | 4/0 AWG (24V) / 2/0 AWG (48V) |
Illustrative only. Actual conductor sizing depends on ampacity, cable length, allowable voltage drop, temperature, installation conditions, and applicable code/manufacturer requirements.
Inverter & DC Battery Current Sizing Formulas
Standard electrical conversion from AC output demand to continuous DC battery current with an illustrative 20% planning margin at default 92% inverter efficiency.
Variable Definitions
Continuous_WattsTarget Continuous Inverter Rating(Watts)- Continuous AC output rating with 20% illustrative planning headroom
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 continuous load (at 92% efficiency)
Inverter_EfficiencyDC-to-AC Inversion Efficiency(%)- Internal conversion efficiency of the inverter (default assumption: 92%)
Calculation Notes
- Pure sine wave output is generally preferred for sensitive electronics, motors and variable-speed equipment. Verify the equipment manufacturer's power-quality requirements.
- Illustrative fuse sizing = calculated continuous DC current × selected planning factor (default: 1.25). Final fuse selection must also satisfy the inverter/battery manufacturer's requirements, conductor ampacity, fuse class/interrupt rating, installation conditions, and applicable electrical code.
- Startup current varies by equipment. If available, use the manufacturer's specified starting/inrush requirement or measured startup load. A 3×–5× multiplier is only a rough planning example.
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 an illustrative 20% planning headroom. 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. Startup current varies by equipment; use manufacturer data when available.
Why does a 12V inverter require thicker cables than a 48V inverter?
Power equals Voltage multiplied by Current (Watts = Volts × Amps). At 92% efficiency, delivering 2,000 Watts on a 12V system requires approximately 181.2 Amps of DC current (requiring heavy conductor gauges like 2/0 AWG). On a 48V system, delivering the same 2,000 Watts requires only 45.3 Amps of current (requiring much thinner conductors like 4 AWG). Actual conductor sizing depends on cable length, allowable voltage drop, and installation conditions.
What is the difference between Pure Sine Wave and Modified Sine Wave inverters?
Pure Sine Wave inverters produce smooth alternating current identical to grid utility power. Modified Sine Wave inverters produce stepped square-wave power that may cause audible buzzing, excess heat, or performance issues in certain motorized equipment or sensitive power supplies. Pure sine wave output is generally preferred for sensitive electronics, motors and variable-speed equipment. Verify the equipment manufacturer's power-quality requirements.
What size DC fuse do I need for an inverter?
Illustrative fuse sizing = calculated continuous DC current × selected planning factor (e.g., 1.25×). For example, a 1,000W continuous inverter load on a 12V battery draws approximately 90.6A DC at 92% efficiency; multiplying by 1.25 gives 113.3A, for which a 125A fuse is an illustrative selection. Final fuse selection must also satisfy the inverter/battery manufacturer's requirements, conductor ampacity, fuse class/interrupt rating, installation conditions, and applicable electrical code.
Methodology and Model Basis
Inverter calculations use inductive motor starting characteristics and general 75°C copper ampacity references. See our methodology and sources.
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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.