Watts to amps calculator
Amps = watts ÷ volts. Pick the voltage, enter the watts (or amps), and if an AC load runs off a battery through an inverter, include the inverter loss to see what the battery really supplies.
Enter your measurements
- Energy per hour of running
- 1 kWh
| Voltage | Amps | Amps × volts |
|---|---|---|
| 12 V | 83.3 A | 1,000 W |
| 24 V | 41.7 A | 1,000 W |
| 48 V | 20.8 A | 1,000 W |
| 120 V | 8.3 A | 1,000 W |
| 240 V | 4.2 A | 1,000 W |
1,000 W ÷ 12 V = 83.3 A
Quick answers for common sizes
| Example | Answer |
|---|---|
| How many amps is 1000 watts at 12 volts | 83.3 A (92.6 A through an inverter) |
| How many amps is 1500 watts at 120 volts | 12.5 A |
| 400 watts to amps at 12V | 33.3 A |
Amps for common loads at the voltage above
| Power | Current |
|---|---|
| 100 | 8.3 A |
| 300 | 25 A |
| 500 | 41.7 A |
| 1000 | 83.3 A |
| 1500 | 125 A |
| 2000 | 166.7 A |
| 3000 | 250 A |
The three conversions people look up most are worked through on their own pages: how many amps is 1000 watts at 12 volts, how many amps is 1500 watts at 120 volts and 400 watts to amps at 12V.
The formula
Power in watts is voltage times current. Rearranged, current is power divided by voltage. That is the same relationship the extension service uses when a label lists amps but not watts — multiply amps by volts.
amps = watts ÷ volts watts = amps × volts battery amps through an inverter = watts ÷ inverter efficiency ÷ battery volts
The same load pulls ten times the current at 12 V that it does at 120 V. That is why low-voltage systems need short, heavy cables and why bigger off-grid systems move to 24 V or 48 V: half or a quarter of the current for the same power.
Watts to amps at common voltages
| Watts | 12 V | 24 V | 48 V | 120 V |
|---|---|---|---|---|
| 100 W | 8.3 A | 4.2 A | 2.1 A | 0.8 A |
| 200 W | 16.7 A | 8.3 A | 4.2 A | 1.7 A |
| 400 W | 33.3 A | 16.7 A | 8.3 A | 3.3 A |
| 500 W | 41.7 A | 20.8 A | 10.4 A | 4.2 A |
| 1,000 W | 83.3 A | 41.7 A | 20.8 A | 8.3 A |
| 1,500 W | 125 A | 62.5 A | 31.3 A | 12.5 A |
| 2,000 W | 166.7 A | 83.3 A | 41.7 A | 16.7 A |
| 3,000 W | 250 A | 125 A | 62.5 A | 25 A |
When amps × volts isn’t the whole story
- Motors and compressors. AC motor loads can draw more current than their watts suggest. For those, use the amps printed on the nameplate rather than converting watts.
- Start-up surge. A fridge, pump or air conditioner draws several times its running current for a moment as it starts. That sizes the inverter or generator, not the battery.
- Battery voltage changes. A “12 V” battery sits around 12–13 V in use and lower near empty, so the amps for a fixed wattage creep up as it discharges. LiFePO4 is nominally 12.8 V.
- Panel watts to charging amps. An MPPT charge controller turns panel watts into battery amps by the same formula — Victron’s example is 100 W ÷ 13 V = 7.7 A. The charge controller calculator builds on that.
What you’ll need
- DC clamp meterMid-range price
Clamps around one cable to read DC amps without breaking the circuit — checks what an inverter or fridge actually draws from the battery. Make sure it says DC; many cheap clamps read AC only.
See options on Amazon (opens in a new tab) - Digital multimeterBudget price
Reads battery voltage, panel open-circuit voltage and continuity. The first tool to reach for when a solar system is not charging.
See options on Amazon (opens in a new tab) - Plug-in electricity usage monitorBudget price
Plugs in between the wall and a 120 V appliance and shows real watts and kWh over a day — the honest way to fill in a load list, especially for fridges that cycle on and off.
See options on Amazon (opens in a new tab)
As an Amazon Associate we earn from qualifying purchases. Links to products are affiliate links — they cost you nothing extra and help keep these calculators free.
Frequently asked questions
How many amps is 1000 watts?
It depends on the voltage: 83.3 A at 12 V, 41.7 A at 24 V, 20.8 A at 48 V and 8.3 A at 120 V. From a 12 V battery through a 90% inverter it is about 92.6 A — see how many amps is 1000 watts at 12 volts.
How do I convert amps to watts?
Multiply amps by volts. A 120 V appliance labeled 3 A uses about 360 W; a 12 V fridge drawing 4 A uses 48 W.
How many amps does a 100 watt solar panel produce?
Through an MPPT controller into a 12 V battery, up to about 100 W ÷ 13 V ≈ 7.7 A in full sun (Victron’s worked example). Most of the day it makes less. The solar panel output calculator gives the daily total.
Why does 12 V need such thick cable?
Because the current is ten times higher than at 120 V for the same power, and cable heating rises with current. Wire and fuse sizing comes from ampacity tables and the equipment manual — have a qualified installer check them.
Related guides
Sources
- Virginia Cooperative Extension, BSE-301: Estimating Appliance and Home Electronic Energy Use (2020) (opens in a new tab) — Wattage × hours ÷ 1,000 = kWh per day; watts = amps × volts when only amps are listed; a refrigerator runs at full wattage about a third of the time; typical nameplate wattages.
- Victron Energy — Energy Unlimited (book) (opens in a new tab) — Lead-acid charge efficiency 80–95% (85% suggested as a starting value); battery energy efficiency about 75% for full cycles, about 89% in partial state of charge; inverter efficiencies above 90%.
- Victron Energy — Which solar charge controller: PWM or MPPT? (2020) (opens in a new tab) — MPPT output current = panel watts ÷ battery voltage (100 W ÷ 13 V = 7.7 A); a PWM controller pulls the panel down to battery voltage (81 W from a 100 W panel at 25 °C, about the same as MPPT at 75 °C); temperature-coefficient method; example panel Voc 21.6 V, −0.35 %/°C.