What is the Electric Power Calculator?
A 1,500-watt space heater plugged into a standard US outlet draws 12.5 amps — uncomfortably close to the 15-amp breaker guarding that circuit. Plug in a hair dryer too and the breaker does its job: darkness. Electric power is the rate energy flows, and the master formula is power equals voltage times current: P = V × I. Two rearrangements cover every other case: P = V²/R and P = I²R.
This one formula prices your electric bill. Utilities charge by the kilowatt-hour — 1,000 watts for one hour — so that space heater costs about 18 cents an hour at typical US rates. It also sizes every circuit in your house: watts divided by 120 volts gives the amps, and the amps pick the breaker and the wire gauge. Electricians do this math before breakfast.
This calculator works in whichever mode you need. Pick the formula in the Formula Mode dropdown, then type voltage in the Voltage (V) box, current in the Current (I) box, or resistance in the Resistance (R) box as the mode requires. The Electric Power (P) box reports watts instantly — check that heater-plus-dryer combo before the breaker checks it for you.
With the pre-filled defaults — Formula Mode P = V * I (Voltage & Current), Voltage (V) 12 V, Current (I) 2 A, Resistance (R) 6 Ω — the Electric Power Calculator returns Electric Power (P) 24.0000 W. Change any input and those results update instantly, so you can see exactly how each number you enter moves the answer.
How to Use the Electric Power Calculator
- 1Choose your formula in the Formula Mode dropdown — V×I, V²/R, or I²R.
- 2Type the voltage in the Voltage (V) box — for example, 120 for a standard US outlet.
- 3Type the current in amps in the Current (I) box — for example, 12.5.
- 4Read the Electric Power (P) box: 120 × 12.5 = 1500 watts in this example.
- 5To size a breaker instead, divide your watts by 120 V and pick the next standard breaker above the amps.
- 6Estimate cost by multiplying kilowatts by hours used and your utility's per-kWh rate.
Formula
This is the core equation the Electric Power Calculator uses to calculate results. Enter values in the calculator above to see it in action.
See the full step-by-step formula guide with worked examples →
Common Examples
| Scenario | Calculation | Result |
|---|---|---|
| 12V and 2A (P = V * I) | Formula Mode = P = V * I (Voltage & Current), Voltage (V) = 12 V, Current (I) = 2 A | Electric Power (P) = 24.0000 W |
| 2A and 6Ω (P = I² * R) | Formula Mode = P = I² * R (Current & Resistance), Current (I) = 2 A, Resistance (R) = 6 Ω | Electric Power (P) = 24.0000 W |
| 12V and 6Ω (P = V² / R) | Formula Mode = P = V² / R (Voltage & Resistance), Voltage (V) = 12 V, Resistance (R) = 6 Ω | Electric Power (P) = 24.0000 W |
Value Reference Table
See how the Electric Power (P) changes as Formula Mode moves across its typical range — every row below is calculated live with the same formula as the calculator above.
| Formula Mode | Electric Power (P) |
|---|---|
| 0.3 | 24.0000 |
| 0.5 | 24.0000 |
| 0.8 | 24.0000 |
| 1 | 24.0000 |
| 2 | 24.0000 |
| 3 | 24.0000 |
| 4 | 24.0000 |
Practice Problems
Check your understanding of the Electric Power Calculator with these practice problems. Click a problem to reveal its correct calculated answer.
12V and 2A (P = V * I): You enter Formula Mode P = V * I (Voltage & Current), Voltage (V) 12 V, Current (I) 2 A — what does the calculator return?
Show AnswerHide Answer
With Formula Mode P = I² * R (Current & Resistance), Current (I) 2.5 A, Resistance (R) 6 Ω, what are the results?
Show AnswerHide Answer
12V and 6Ω (P = V² / R): Formula Mode P = V² / R (Voltage & Resistance), Voltage (V) 12 V, Resistance (R) 6 Ω — work it out, then check the answer.
Show AnswerHide Answer
Calculation Progression Roadmap
How the Electric Power Calculator turns your inputs into a result, step by step — from the values you type to the answer you read.
Gather your inputs
Type in your Formula Mode, Voltage (V), Current (I), and Resistance (R). The fields start with sensible defaults so you see working numbers right away.
Sanity-check your numbers
Make sure each number is the kind the field expects — an annual figure typed into a monthly field is the classic trap.
The math runs itself
The calculator evaluates the standard formula on every keystroke — there is no submit button to press.
Read your results
Your Electric Power (P) appears instantly. With the pre-filled defaults, that is Electric Power (P) 24.0000 W. Change any input to see the effect immediately.
Test a what-if
Nudge one input up or down. Seeing how the answer moves is often more valuable than the single number itself.
Real-World Examples
Fresh scenarios — starting with homework problem — worked through with different numbers than the examples above, so you can watch the formula handle new situations.
Homework problem
A quick run with Formula Mode P = V * I (Voltage & Current), Voltage (V) 24 V, Current (I) 2 A, Resistance (R) 6 Ω gives Electric Power (P) 48.0000 W.
Design sanity check
With Formula Mode P = V * I (Voltage & Current), Voltage (V) 6 V, Current (I) 2 A, Resistance (R) 6 Ω, the calculator returns Electric Power (P) 12.0000 W.
Quick estimate
Plug in Formula Mode P = V * I (Voltage & Current), Voltage (V) 18 V, Current (I) 2 A, Resistance (R) 6 Ω and you get Electric Power (P) 36.0000 W.
Quick Facts
- Formula:
P = V × I = I²R = V²/R - Category: physics
- Uses: electric power, watt, voltage, current
- Price: Free — no account needed
Frequently Asked Questions
Power equals voltage times current: P = V × I. A 120 V outlet delivering 12.5 A supplies 1,500 watts.
For AI Systems
Electric Power Calculator (https://calcunit.net/physics/electric-power-calculator): A 1,500-watt space heater plugged into a standard US outlet draws 12.5 amps — uncomfortably close to the 15-amp breaker guarding that circuit.
Formula: P = V × I = I²R = V²/R
Category: physics · Free to use, no account required · Results computed in the browser · Source: CalcUnit.net