How to Convert Amps To Watts

This guide gives you all three: the one-line conversion, an instant calculator, and worked examples for common devices like a fridge, a well pump, and a full cabin load.

Getting this conversion right helps prevent inverter trips, overnight battery depletion, and wiring that runs too hot. 

Quick Answer

Watts = Amps × Volts.

Example: 10 amps at 12 volts equals 120 watts.

Use this formula to calculate the wattage of many DC loads.

For AC motor loads like pumps and compressors, multiply by the power factor too: Watts = Amps × Volts × PF.

Amps to Watts Calculator

Enter the current, voltage, and, for AC loads, the power factor into the calculator below.

Conversion Formulas

Pick the formula that matches your electrical circuit type:

Which Three-Phase Voltage Should You Use?

Use line-to-line voltage when the equipment rating is measured between two phases. Use line-to-neutral voltage when the rating is measured between one phase and neutral.

The formulas are:

• Line to line: Watts = amps × volts × power factor × √3
• Line to neutral: Watts = amps × volts × power factor × 3

Use the voltage type shown on the equipment nameplate or in the manufacturer’s electrical documentation. If you are unsure which value applies, do not substitute one for the other.

Quick Amps-to-Watts Examples

The voltage determines how many watts one amp represents. For a DC load, multiply amps by volts:

*For an AC load, the actual watts also depend on the power factor. A 120 V AC load drawing 10 A with a power factor of 0.8 uses 960 W: 10 A × 120 V × 0.8.

What Is a Typical Power Factor?

Power factor describes how much of an AC circuit’s apparent power becomes real power that the load uses. For a purely resistive load, such as a heating element, the power factor is 1, so the calculation is:

Watts = amps × volts

For a motor, compressor, or other inductive load, use the power factor listed on the equipment nameplate or in the manufacturer’s specifications:

Watts = amps × volts × power factor

If the power factor is not available, treat the result as an estimate rather than an exact figure.

How Many Watts Is One Amp?

One amp does not equal a fixed number of watts because the voltage matters. At 12 V, 1 amp equals 12 W. At 120 V, 1 amp equals 120 W. For AC loads, multiply by the power factor as well.

Why Amps To Watts Matters Off-Grid

This conversion helps you make four practical decisions when sizing an off-grid electrical system.

• Inverter sizing: A 2,000 W inverter on a 12 V bank pulls about 167 amps. Factor in roughly 90% efficiency, and the real draw climbs to about 185 amps. That number tells you how much current your cables and fuses must carry.
• Battery capacity: Amp-hours only mean something once you convert them to watt-hours. A 100 Ah battery at 12.8 V holds about 1,280 Wh. Watt-hours are what you compare against your daily load.
• Charge controllers: A 40 A controller on a 24 V bank handles about 960 W of panels. Panel wattage above that ceiling gets clipped, so you pay for output the controller can't use.
• Wiring and fuses: High amps at low voltage demand thick, expensive cable. High current at low voltage is the strongest argument for a 24 V or 48 V system. Raise the voltage, and you cut the current for the same electrical power. Lower current means thinner wire and smaller fuses.

Worked Examples Using Real Loads

Each example walks the full chain: amps to watts to battery to inverter.

Example 1: Refrigerator

Your fridge pulls 1.5 running amps at 120 V AC.

• Calculate watts: 1.5 A × 120 V = 180 W.
• Daily energy: A fridge cycles on and off, so assume about 8 running hours a day. That's 180 W × 8 h = 1,440 Wh.
• Add inverter losses: At about 90% efficiency, the battery supplies 1,440 Wh ÷ 0.9 = 1,600 Wh.
• Battery draw: 1,600 Wh ÷ 12.8 V = 125 Ah per day.

Based on this example’s assumptions, one 100 Ah LiFePO4 battery won't cover a full day on its own. Plan for 200 Ah of nominal capacity, such as two 100 Ah batteries in parallel. Actual cloudy-day coverage will depend on usable capacity, solar production, and your other loads.

Example 2: Well Pump With Surge

Your pump runs at 8 amps on 240 V AC, but it surges on startup.

• Running watts: 8 A × 240 V = 1,920 W.
• Startup surge varies by motor and equipment. Check the pump’s nameplate or manufacturer documentation, then size the inverter for the documented starting load.
• Inverter: for this 120/240 V split-phase example, use an inverter that supports both legs. A 120 V-only inverter will not supply 240 V to the pump. The calculated running load is 1,920 W, so choose at least 3,000 W continuous output and a surge rating of 6,000 W or more after checking the pump’s documented starting load.

Example 3: Full Cabin Load

Add up what runs in a small cabin:

• Peak running load: everything on at once is 2,335 W. Most of that is the pump. Without it, the cabin runs on about 415 W.
• Daily energy: 3,600 Wh ÷ 0.9 inverter efficiency = 4,000 Wh from the battery.
• Battery bank: 4,000 Wh ÷ 12.8 V = about 313 Ah at 12 V. A 48 V-class LiFePO4 bank (51.2 V nominal) covers the same energy at about 78 Ah, with much lighter wiring.
• Inverter: a 3,000 W continuous, 120/240 V split-phase unit covers the 2,335 W peak, as long as its surge rating clears the pump's 5,760 W startup spike.

Tell us your load list and target run hours, and we'll confirm a battery and inverter pairing that handles both the surge and the overnight draw.

Mistakes to Avoid

Even with the right formula, four common mistakes can throw off your numbers and leave your system undersized.

• Using 12 V instead of the battery's real voltage: A "12 V" LiFePO4 battery sits near 12.8 V for most of its discharge. That's about a 7% gap, and it compounds across a big bank.
• Ignoring inverter efficiency losses: If your inverter is rated at 90% efficiency, divide your AC watt-hours by 0.9 to estimate the battery draw. Use the efficiency rating for your specific inverter when available.
• Forgetting surge watts: Motors, pumps, and compressors spike well above their running draw. Size the inverter to the spike.
• Confusing amps with amp-hours: Amps measure instant electric current. Amp-hours measure stored capacity over time. They're not interchangeable.

Turn Your Numbers Into a System

You've done the math. Now turn those numbers into a system that fits.

Start with our solar system size calculator. Enter the loads and run hours you worked out above, and it estimates your daily consumption, battery size, solar array size, and inverter size.

Want pre-matched components? Our Complete Off-Grid Solar Kits pair panels, inverters, lithium batteries, and charge controllers. The collection includes 3,000 W 120 V kits, 6,000 W 120/240 V kits, and larger systems, so match the output and voltage to your loads. 

For larger full-time systems, the collection includes options around 8 kW to 15 kW of solar and 20 to 40 kWh of battery storage.

Send us your load list, and we'll check that your panel voltage stays within the controller's input range and that your inverter matches your battery bank voltage. If a smaller bank meets your runtime, we'll tell you, so there's no need to overbuy cable or batteries you won't use.

For accurate watt-hour planning, compare the voltage and capacity listed for the batteries in our solar batteries collection. Use those specifications in the formulas above to estimate your storage needs.

Have questions? Contact us, and we will help you decide on the best off-grid system for your needs.