Students
Check homework, learn Ohm's law, and see the working behind every current calculation before an exam.
Current Calculator Online
Work out electric current in amps from power, voltage, resistance, and power factor. One free tool for DC, single phase, and three phase circuits, right here in your browser.
Current calculator tool
Enter your values — Single Phase AC
Current
— A
Fill in every field to see the current, the exact equation used, and a full breakdown.
Every calculation runs locally with plain JavaScript — nothing you type leaves your device. Results use the standard electrical formulas under ideal, balanced conditions and are intended for reference and study. For live installations, follow your local wiring rules and consult a qualified electrician.
Four Simple Steps
How To Use the Current Calculator
From a wattage rating or a voltage and resistance to the current in amps, in a few seconds.
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Pick a Method
Choose Ohm's law, current from power and voltage, single phase AC, three phase AC, or motor horsepower. The calculator shows only the fields that method needs.
Tip: single phase is the safe default -
Enter Your Values
Type the power, voltage, resistance, or power factor, and pick the unit you actually have — watts or kilowatts, volts or kilovolts. No manual conversion needed.
Tip: switch W to kW right in the field -
Read the Current
The amperage appears instantly as you type, alongside the exact equation, cross checks such as apparent power, and a circuit sizing guide for breakers and cable.
Tip: results update live -
Save or Share It
Copy the result and its working in one click, or grab a share link that reopens the calculator with your exact figures already filled in.
Tip: recent results are kept for you
Built for Students and Pros
Everything the Current Calculator Can Do
Nine reasons students, electricians, and engineers keep this current calculator bookmarked.
Five Calculation Modes
Ohm's law, current from power and voltage, single phase AC, three phase AC, and motor horsepower, all in one place with the right inputs for each.
Live Results
The current updates as you type, so you can see how changing the voltage or power factor moves the amperage in real time.
Built In Unit Switching
Enter watts, kilowatts, megawatts or horsepower, volts or kilovolts, milliohms through megohms. The calculator converts everything for you.
Three Phase Ready
The three phase mode uses the correct root three factor for line current, so panel and motor figures come out right.
Power Factor Aware
Real AC loads are not perfect. Enter a power factor and the calculator reflects how it raises the current a load pulls.
Private by Design
Nothing you type is uploaded. Every calculation runs on your own device, so your figures never touch a server.
Works on Any Device
Phone, tablet, laptop, or desktop. The current calculator is fully responsive and needs only a modern web browser.
Circuit Sizing Guide
Every result adds a design current at 125 percent, a typical breaker rating, and an indicative copper conductor size for a sanity check.
Copy, Share and Recall
Copy the answer with its working, share a link that reopens your exact figures, and pick up recent calculations where you left them.
A Note on the Formulas
Current Calculator uses the standard relationships between current, voltage, power, and resistance. Ohm's law gives current as voltage divided by resistance. For a DC or resistive load, current equals power divided by voltage. For alternating current you also divide by the power factor, and for a balanced three phase supply you divide by the square root of three multiplied by the line voltage and power factor. These results assume ideal, balanced conditions. Real installations add cable resistance, temperature, and starting surges, so treat the figures as a solid starting point rather than a final design.
Quick Reference
Current Formulas at a Glance
The five equations behind the current calculator, and when to reach for each one.
| Situation | Formula | You need | Example |
|---|---|---|---|
| Ohm's law | I = V / R | Voltage, resistance | 12 V ÷ 10 Ω = 1.2 A |
| Current from power (DC) | I = P / V | Power, voltage | 1500 W ÷ 12 V = 125 A |
| Single phase AC | I = P / (V × PF) | Power, voltage, power factor | 1500 W ÷ (230 V × 0.9) = 7.25 A |
| Three phase AC | I = P / (√3 × V × PF) | Power, line voltage, power factor | 5000 W ÷ (1.732 × 400 V × 0.9) = 8.02 A |
| Motor from horsepower | I = (HP × 746 / η) / (√3 × V × PF) | Horsepower, voltage, efficiency, power factor | 5 hp at 400 V, 89%, 0.86 PF = 7.03 A |
Who It Is For
Who Uses the Current Calculator
Six kinds of people open this page every day, and every one of them leaves with the amperage they were looking for.
Electricians
Size a circuit fast by turning a load rating into an approximate current for single phase or three phase supplies.
Engineers
Run a quick sanity check on a motor or panel current with the correct three phase and power factor terms.
Hobbyists
Figure out how many amps a device, LED strip, or 3D printer draws before wiring it up on the bench.
Home Owners
Understand the current an appliance uses from the wattage on its label, and whether a circuit can handle it.
Solar & EV Users
Estimate panel and charger currents from watts and volts to plan cabling, fuses, and connectors.
Guides & Tutorials
Latest From the Current Calculator Blog
Ohm's law, power factor, three phase basics, and practical current calculations explained clearly.
Guides
How to Calculate Current: A Complete Beginner Guide
Work out current from power, voltage, and resistance, explained step by step for beginners.
Basics
Ohm's Law Explained: Voltage, Current and Resistance
The most useful relationship in electronics, and how to rearrange it for any value.
Guides
How to Find Current From Power and Voltage
Use the current from power formula to turn watts and volts into amps.
Three Phase
Three Phase Current Calculation Made Simple
The root three formula for line current and how to apply it to motors.
Three Phase
Single Phase vs Three Phase: Current and Power
How current differs between supplies, and when each one is used.
AC Theory
What Is Power Factor and Why It Changes Your Current
Real, reactive, and apparent power, and how power factor raises current.
How the Calculation Works
Accurate Amps, Worked Out in Your Browser
The current calculator takes the values you type, applies the correct standard formula for the method you chose, and returns the current in amps. Ohm's law divides voltage by resistance. The power method divides power by voltage. The AC methods add the power factor, and the three phase method adds the square root of three for line current. You can read more about who builds this tool and why.
Alongside the amperage, the tool shows the exact equation with your numbers filled in, plus useful extras such as apparent power in volt amps or an equivalent resistance. That makes it as much a learning aid as a calculator, which is the point.
Because everything happens locally, there is no upload, no wait, and no privacy trade off. The standards we hold our guides to are set out in our editorial policy.
What People Say
Trusted by Students and Trades
Learners, electricians, and engineers use Current Calculator to check amps quickly.
Quick Answers
Current Calculator FAQs
The questions people ask most before they run their first calculation with Current Calculator.
For a DC or resistive load, divide the power in watts by the voltage in volts. A 1500 watt heater on 12 volts draws 125 amps. For AC you also divide by the power factor, and the calculator does this for you when you pick a single phase or three phase mode.
Yes, completely free. There is no signup, no login, and no payment. Open the page, pick a method, type your values, and read the current right away.
Line current equals the total real power divided by the square root of three, times the line to line voltage, times the power factor. In the calculator, choose the three phase mode and enter power, voltage, and power factor, and it applies the root three factor automatically.
No. Every calculation runs locally in your browser with plain JavaScript. Nothing you type is uploaded, and there is no tracking of the values you enter.
Resistive loads like heaters and incandescent bulbs are close to 1. Motors and many electronic loads are often between 0.7 and 0.9. If a nameplate gives a power factor, use that value. Otherwise 0.9 is a reasonable starting estimate.
Yes. Pick the three phase mode, enter the motor power in watts, the line voltage, and the power factor from the nameplate. The result is the full load line current. Remember that starting current can be several times higher.
Ohm's law states that current equals voltage divided by resistance, or I = V / R. It links the three core quantities of any simple circuit. The Ohm's law mode uses it directly, and you can rearrange it to find voltage or resistance too.
First convert kilowatts to watts by multiplying by 1000, then divide by the voltage, and for AC divide by the power factor as well. Enter the power in watts in the calculator and it handles the rest. Our kW to amps guide walks through each supply type.
The calculator assumes ideal, steady conditions. In reality, voltage sags under load, power factor varies, and motors surge on startup. Treat the result as a close estimate and always allow headroom when sizing protection.
No. The current calculator runs entirely in your web browser. There is nothing to download or install, and it works on Windows, macOS, Linux, Android, and iOS.
Use the line to line voltage, for example 400 V or 415 V on many systems. The root three factor in the formula accounts for the relationship between line and phase quantities, so you do not need to convert first.
No. It is a study and reference tool. For real wiring, protection, and safety decisions, always follow your local regulations and use a qualified electrician. See our disclaimer for the full scope.
Work Out Your Current Now
Free, private, and instant. Pick a method, enter your values, and read the amps in seconds.