Amps to kWh Calculator
Convert a current draw to kilowatt-hours using the voltage and the hours, then price it.
Updated
Leave at zero to see the energy without a cost.
Energy used
3.600 kWhof energy
1,800 W drawn for 2 h
- Power
- 1,800 W
- Energy
- 3.600 kWh
- Cost
- $0.61
- If it ran all day
- 43.20 kWh
Amps alone say nothing about a bill. A 15 A circuit and a 15 A load are different claims, and only the second one, held for a known time, becomes kilowatt-hours.
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In short
How do you convert amps to kWh?
In two steps. Multiply amps by volts for watts, then multiply by hours and divide by a thousand. 15 A at 120 V is 1,800 W, and running for two hours that is 3.6 kWh — about 61 cents at 17 cents a unit.
A breaker rating is a ceiling, not a draw. A 15 A circuit rarely carries 15 A.
How to use the amps to kWh calculator
Amps, volts, hours. Those three give kilowatt-hours, and leaving any of them out leaves the question unanswerable. That is the whole content of this page, and it is why "how many kWh is 15 amps" has no answer as asked.
Current is a rate of charge flow. It says nothing about energy until you know the voltage pushing it, and nothing about total energy until you know for how long. A 15 amp draw for a second and a 15 amp draw for a day are the same current and wildly different bills.
1,800 W
15 amps at 120 volts
amps times volts
3.6 kWh
That load for two hours
watts times hours, over 1,000
61 cents
At 17 cents a kilowatt-hour
the whole two hours
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The most common version of this question comes from a breaker panel, and it rests on a misunderstanding worth naming. A 15 amp breaker does not mean the circuit draws 15 amps. It means the circuit will disconnect if it ever tries to draw more. What it actually draws is whatever is plugged into it, which is usually a fraction of that.
For a real figure you need a measured current. A plug-in monitor gives it for a single appliance and a clamp meter gives it for a circuit, and either is worth more than any amount of arithmetic on nameplate ratings, because most appliances cycle rather than running continuously.
- 1 A at 120 V, all day
- 2.88 kWh
- 5 A at 120 V, all day
- 14.4 kWh
- 10 A at 120 V, one hour
- 1.2 kWh
- 15 A at 120 V, two hours
- 3.6 kWh
- 15 A at 120 V, eight hours
- 14.4 kWh
- 30 A at 240 V, four hours
- 28.8 kWh
The 30 amp row is a clothes dryer or a small electric vehicle charger, and at 28.8 kWh it is roughly what an average household uses in a whole day. High-current 240 volt circuits are where domestic electricity consumption actually concentrates.
Work out the current first
If you have a resistance or a wattage rather than a measured current, the volts to amps page gets you the amps figure this calculation starts from.
Open volts to amps →Currents converted to kilowatt-hours at two common supply voltages across a range of running times, with the cost at seventeen cents a unit.
| Current | Supply | Power | Hours | kWh | At $0.17 |
|---|---|---|---|---|---|
| 1 A | 120 V | 120 W | 24 | 2.88 | $0.49 |
| 2 A | 120 V | 240 W | 8 | 1.92 | $0.33 |
| 5 A | 120 V | 600 W | 4 | 2.40 | $0.41 |
| 5 A | 120 V | 600 W | 24 | 14.40 | $2.45 |
| 10 A | 120 V | 1,200 W | 1 | 1.20 | $0.20 |
| 12 A | 120 V | 1,440 W | 3 | 4.32 | $0.73 |
| 15 A | 120 V | 1,800 W | 2 | 3.60 | $0.61 |
| 15 A | 120 V | 1,800 W | 8 | 14.40 | $2.45 |
| 20 A | 240 V | 4,800 W | 2 | 9.60 | $1.63 |
| 30 A | 240 V | 7,200 W | 4 | 28.80 | $4.90 |
| 40 A | 240 V | 9,600 W | 6 | 57.60 | $9.79 |
Why a 15 amp circuit is not a 15 amp load
A breaker is a safety device, not a meter. Its rating describes the point at which the wiring behind it would start to overheat, and its job is to disconnect before that happens. Nothing about it describes what the circuit normally carries.
- Breaker rating
- 15 A
- If it carried that for 8 hours
- 14.4 kWh
- Actual measured draw
- about 1.2 A
- The same 8 hours
- 1.15 kWh
- Overestimate from the breaker
- over twelve times
- What to measure
- the draw, not the rating
A television, a lamp and a router together sit around an amp. Converting the breaker rating instead would put the room at more than twelve times its real consumption, and that error compounds across every circuit in a house.
The eighty percent rule points the same way from the other side. A circuit is designed so that a continuous load never exceeds eighty percent of its rating, which means a 15 amp circuit is intended to carry no more than 12 amps for any sustained period, and usually carries far less.
Measuring rather than estimating
Almost every appliance draws less than its nameplate over a real day, because most of them cycle. A fridge rated at 150 watts runs perhaps a third of the time; a heater with a thermostat does the same. Nameplate arithmetic consistently overstates consumption for exactly this reason.
Do
- Measure the actual current with a clamp meter or plug monitor
- Use the hours the load is drawing, not the hours it is on
- Take your rate from a bill rather than a headline tariff
- Check whether the circuit is 120 or 240 volts before converting
Don't
- Convert a breaker rating into a consumption figure
- Add up nameplate ratings and treat the total as a draw
- Assume an appliance runs continuously when it has a thermostat
- Apply a 120 volt figure to a dryer or oven circuit
The voltage error is the one that doubles or halves everything. Dryers, ovens, water heaters and vehicle chargers are on 240 volt circuits, so the same current is twice the power. Converting a 30 amp dryer at 120 volts understates it by exactly half.
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The formula, worked line by line
Two multiplications and a division, in a fixed order. Writing them out makes the missing-information problem obvious: neither step can be skipped, and each needs a quantity the current does not carry.
“Amps tell you how fast charge is moving. Volts tell you how hard. Hours tell you for how long. Energy needs all three.”
That is also why a bill is denominated in kilowatt-hours rather than in amps. The meter is counting energy delivered, which is the only quantity that accumulates.
watts = amps x volts
kWh = (watts / 1,000) x hours
15 A x 120 V = 1,800 W
(1,800 / 1,000) x 2 = 3.6 kWh
cost = kWh x rate- Measured draw
- 12.5 A at 120 V
- Power
- 1,500 W
- Running 6 hours a day
- 9 kWh
- At $0.17 per kWh
- $1.53 a day
- Over 120 days
- $183.60
- One room, one season
- about $184
That is for a heater running six hours a day at full output. A thermostat cutting it to half duty halves the figure, which is why the measured average current matters more than the nameplate rating for any appliance that cycles.
Why the voltage has to be right
Domestic circuits run at two voltages and the higher one is where the heavy loads sit. Ovens, dryers, water heaters and vehicle chargers are 240 volt in North America; almost everything else is 120. Using the wrong figure is a clean factor-of-two error in whichever direction you chose.
Where household consumption concentrates
- Lighting circuit
- 1 to 3 A at 120 V
- Kettle or toaster
- 10 to 13 A at 120 V
- Space heater
- 12.5 A at 120 V
- Clothes dryer
- 20 to 30 A at 240 V
- EV charger, level 2
- 30 to 48 A at 240 V
The bottom two rows draw more power than everything above them combined, and they are the reason a home with an electric vehicle often needs a service upgrade rather than just another circuit.
One habit worth keeping: whenever somebody quotes amps as if it were a cost, ask what voltage and for how long. Without both, the figure cannot become money.
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Questions people ask
How do I convert amps to kWh?
Multiply amps by volts to get watts, then multiply by the hours and divide by a thousand. 15 amps at 120 volts is 1,800 watts, and two hours of that is 3.6 kilowatt-hours. Current alone cannot give energy: it needs both the voltage and the running time.
How many kWh does a 15 amp circuit use?
That depends entirely on what is plugged into it. A 15 amp breaker is a ceiling, not a draw — it disconnects the circuit if consumption ever exceeds that. A living room circuit on a 15 amp breaker typically draws around one amp, which is a twelfth of the rated maximum.
Do I use 120 or 240 volts?
Whichever the circuit runs at. In North America lighting and general outlets are 120 volts, while dryers, ovens, water heaters and electric vehicle chargers are 240. Using the wrong one is a factor-of-two error, so check the appliance or the breaker before converting.
Why does my calculation exceed my actual bill?
Almost certainly because the appliance cycles. A fridge rated at 150 watts runs perhaps a third of the time, and anything with a thermostat behaves the same way. Nameplate arithmetic assumes continuous operation, which very few appliances do, so it consistently overstates real consumption.
How do I measure the actual current?
A plug-in energy monitor sits between the socket and one appliance and reads its draw directly. A clamp meter goes around a single conductor and reads a whole circuit without disconnecting anything. Either gives a real figure, which is worth more than any calculation from ratings.
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