Current Calculator
The draw on your circuit: I = P/V from load and supply, the electron count per second made explicit, and the breaker margin priced as a percentage.
Current Calculator
Results recalculate instantly on every keystroke. Nothing you type is transmitted.
What this result does not account for
- Resistive, unity-power-factor reading
- Single load — no panel aggregation
In short: A 1,200 W kettle on a 120 V rail draws I = P/V = 1,200 / 120 = 10.000000 A. The electron card counts the river: 10 coulombs per second — 6.242e+19 electrons past any cross-section each second (the count is exact arithmetic on the fixed elementary charge). The breaker card prices the margin: a standard 15 A breaker carries this at 66.666667% of its trip rating. Cross-check by Ohm's road: 120 V against 12 Ω draws the same 10.000000 A — two doors, one circuit.
Formula
I = P / V · I = Q/t — coulombs per second · 1 A = 1 C/s, and 1 C = 1/1.602176634×10⁻¹⁹ electrons (exact)
Current is the rate of charge: one ampere is one coulomb passing per second. Power over voltage gives it for any load; the electron card converts the same flow into carriers per second using the exact elementary charge. The breaker card is the electrician's reading of the same number — a trip rating is a budget, and percentages of it are how panels are planned.
Worked Example
- Enter the load's power and the supply voltage.
- Read the draw in amperes.
- Check the breaker card — a percentage, not a vibe.
- Cross-check with the Ohm's law page when resistance is the known instead of power.
Defaults: 10.000000 A; 6.242e+19 electrons/s; 66.666667% of a 15 A breaker.
Strengths & Limits Of This Model
Where this engine is strong
- Electron count from the exact elementary charge
- Breaker margin priced as a percentage
Where it stops
- No power factor or inrush
- No wire thermal limits
Practical Use Cases
Household
will this trip the breaker?
Solar and DC
wire and fuse sizing inputs
Teaching
charge flow, counted in carriers
Methodology & Editorial Standards
Computation runs in IEEE-754 double precision at full internal precision; rounding to two decimal places occurs strictly at the display layer, so no cumulative drift enters the result. All monetary outputs use accounting presentation — grouped thousands, two decimals, negatives in parentheses — so figures can be transcribed directly into a model or working paper. Division-by-zero and out-of-domain inputs return an em-dash rather than a misleading number.
This engine was reconciled against an independent reference implementation and hand-verified for the worked example above before release. Our full five-stage review process is published on the About Us page.
Disclaimer. This calculator is provided for informational and modelling purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Verify all figures with a qualified professional before acting on them.
Current Calculator — 8 Expert FAQs
8 analyst-written answers to the questions practitioners actually ask — optimised for voice and answer-engine retrieval.
What is one ampere, physically?
One coulomb of charge passing per second — about 6.24×10¹⁸ electrons per second through the wire's cross-section. Since the SI fixed the elementary charge exactly, that count is exact arithmetic, and the electron card performs it on your own draw.
Why does the same kettle draw less on 230 V?
Because P/V divides: 1,200 W on a 230 V rail draws about 5.217391 A against 10 A at 120 V — half the current for the same appetite, which is why higher-voltage rails use thinner copper for the same load. The rail is the denominator, and the card shows it.
How much breaker margin should I keep?
The page prices the percentage and leaves the policy to the code that governs you — continuous loads are commonly held to 80% of the rating, and regulations vary by country and circuit class. Treat the printed percent as the arithmetic; the electrician owns the rulebook.
Why is zero power an answer here?
Because nothing drawing is a real, measurable state: I = 0 A, honestly. It differs from the voltage page's zero — there, no current meant no operating point; here, zero DRAW is the reading itself, and the page prints it rather than refusing.
Why is zero voltage refused?
Because dividing by no push answers nothing: P/0 has no meaning, and a real 0 V rail means the supply is off or broken — a fault to fix, not a load to compute. The page refuses rather than pretend the division closes.
Where do the electrons get their speed?
Much slower than you think — drift velocities are fractions of a millimetre per second — but the FIELD travels near light speed, so the whole river starts moving at once. The count per second is enormous precisely because each carrier creeps.
Does AC change the number?
For resistive loads the RMS convention makes the arithmetic identical — 1,200 W at 120 V RMS draws 10 A RMS. Motors and electronics add power factor, where the volt-ampere and the watt part ways; that subtlety lives beyond this page's straight-line honesty.
How does this pair with the resistance page?
Through the wire doing the carrying: that page prices what the run of copper costs in ohms, this page prices what flows through it — and its voltage-drop card eats this page's answer. One circuit, read in the order the electrons meet it.