Amps / Watts / Volts Converter
Convert between amps, watts, and volts. Enter any two values to calculate the third, plus energy cost estimates.
About this calculator
This calculator solves for whichever of watts, amps, or volts you leave unset, then estimates the daily, monthly, and annual energy cost of running that load. With the default inputs (watts and volts both entered), Watts is the value that drives the displayed Watts output directly -- since both watts and volts are already provided and positive, the calculator computes amps from them and simply echoes the entered watts figure back as the result, so Watts moves the output one-to-one while Volts has zero effect on the displayed Watts figure in that mode. This can be surprising: you might expect voltage to matter for a "watts" calculation, but once both watts and volts are supplied, the engine treats watts as already known and only uses volts to back out the corresponding amperage, not to adjust the watts value itself.
Daily Usage (hours) increases Daily kWh directly, since energy consumed scales linearly with how many hours per day the device runs at its calculated wattage. Electricity Rate increases Monthly Cost directly too, since the monthly figure is simply daily energy cost (kWh times rate) multiplied by 30. This is a straightforward Ohm's Law and energy-cost calculation -- it doesn't account for power factor on non-resistive loads, standby power draw, or seasonal usage variation.
Inputs
Results
Watts
1,500 W
≈ 25 laptops
How to Use This Calculator
- Enter any two of the three values — Watts, Amps, or Volts — to calculate the third.
- Input Daily Usage (hours) to compute daily kilowatt-hours (kWh).
- Enter your Electricity Rate ($/kWh) to see the daily and annual operating cost.
- Review the calculated Watts and Amps alongside the cost estimates.
- Use this to size extension cords, check outlet capacity, or estimate appliance running costs.
How the result changes with Watts
| Watts | Watts |
|---|---|
| 750 | 750 W |
| 1,125 | 1,125 W |
| 2,250 | 2,250 W |
| 3,750 | 3,750 W |
What each input means
- Watts
- Power in watts. Leave at 0 to calculate from amps and volts.
- Amps
- Current in amps. Leave at 0 to calculate from watts and volts.
- Volts
- Voltage of the circuit (120V standard, 240V heavy appliances).
- Daily Usage
- Average hours per day the device runs.
- Electricity Rate
- Local electricity cost per kilowatt-hour.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersWatts = 1500, Amps = 0, Volts = 120, Daily Usage = 8 = 5 input(s) provided
- Calculate WattsWatts1500 = 1500
- Calculate AmpsAmps12.5 = 12.5
- Calculate VoltsVolts120 = 120
Engine last updated . Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
When both watts and volts are already entered, which one does the calculator treat as fixed?
Watts -- once both Watts and Volts are entered as positive values, the calculator treats watts as already known and only uses Volts to compute the corresponding Amps figure. The displayed Watts output simply echoes back what you entered, so Volts has zero effect on it in that mode.
What role does daily usage play in the energy cost estimate?
Daily Usage (hrs/day) increases Daily kWh in direct proportion, since energy used is calculated as wattage multiplied by hours and divided by 1,000 -- running a device twice as many hours per day doubles the estimated daily, monthly, and annual energy cost, holding wattage and rate constant.
What role does the electricity rate I enter play in the monthly cost estimate?
Electricity Rate increases Monthly Cost directly and proportionally -- Monthly Cost is calculated as daily kWh multiplied by your entered rate, then multiplied by 30, so a higher local electricity rate raises the monthly estimate by exactly that same percentage, holding usage constant.
Can I calculate this using amps and volts instead of entering watts directly?
Yes -- the calculator computes Watts as amps multiplied by volts and uses that calculated value for the energy cost estimates. Watts, Amps, and Volts work as a linked trio — provide any two of the three, leave the third at its default, and the calculator fills in the missing value using the standard electrical relationship between them.
If I type a value into Amps while Watts and Volts are already filled in, does it change anything?
No. In the default configuration, both Watts and Volts already hold positive values, so the calculator treats Amps as the value being solved for and computes it from Watts and Volts directly -- whatever you type into the Amps field is overwritten by that calculation and never factors into any result. To have your entered Amps value actually used, clear Watts or Volts back to 0 first.
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