Calculate electrical current from voltage and resistance, power and voltage, or power and resistance, with exact equations, current-scale conversions.
Last updated
Current calculator Choose the electrical relationship you know, enter the two known values, and solve current in amperes with the exact equation shown.
Known pair
Use this when you know the supply voltage and the load resistance.
Quick examples
A 12 V load with 6 Ω resistance draws 2 A.
Mode behavior
Switching formulas clears the current inputs so each current calculation stays unambiguous.
Result
2.000 A
Voltage and resistance produces 2.000 A from the values you entered.
Voltage
12 V
Resistance
6 Ω
Formula used
I = V / R
I = 12 / 6 = 2 A
How to use this current result
This result is a direct Ohm's law current estimate. If the same resistance stays in the circuit, current rises in step with voltage.
Known pair
Voltage and resistance
Best next step
Check the implied wattage with P = V × I if you need a resistor, fuse, or power-supply sanity check.
Assumption check
This mode assumes the entered resistance is the operating resistance of the load. Real components can drift with temperature and tolerance.
Current scale
This amps calculator also breaks the answer into the unit scale most people actually use when checking small circuits or larger loads.
Amps
2 A
Use amps for wire loading, breaker checks, and general current planning.
Milliamps
2000 mA
Milliamps are easier to read for sensors, LEDs, and small control circuits.
Microamps
2000000 µA
Microamps matter when the solved current is very small or leakage is relevant.
If the same resistance is used at common voltages
These checkpoints keep the solved resistance fixed and show how both current and power would move if the supply voltage changes.
Voltage
Current
Power
Planning note
3.3 V
550.000 mA
1.815 W
lower current and lower power than the solved case. Same resistance assumed.
5 V
833.333 mA
4.1667 W
lower current and lower power than the solved case. Same resistance assumed.
12 V
2.000 A
24 W
Very close to the solved case. Same resistance assumed.
24 V
4.000 A
96 W
higher current and higher power than the solved case. Same resistance assumed.
120 V
20.000 A
2400 W
higher current and higher power than the solved case. Same resistance assumed.
230 V
38.333 A
8816.6667 W
higher current and higher power than the solved case. Same resistance assumed.
What this means
Current tells you how much charge flows through the circuit element. Use it to verify component ratings, estimate wire loading, or check a power budget.
For AC loads that are not simple resistors, treat the result as a planning estimate and confirm the load model, power factor, and datasheet assumptions separately.
Current calculator: solve amps from voltage, resistance, or power relationships
A current calculator solves electrical current in amperes when you know one of three common input pairs: voltage and resistance, power and voltage, or power and resistance. It is useful for quick bench checks, resistor sizing, power-supply planning, and verifying that a circuit stays inside expected current limits.
What this current calculator solves
This page covers three practical ways to solve current. If you know voltage and resistance, it applies Ohm's Law directly. If you know power and voltage, it uses the basic power equation. If you know power and resistance, it derives current from the square-root relationship between power and resistance.
Showing the exact working equation matters because the right formula depends on what you already know about the circuit. The calculator keeps those modes separate so each result stays easy to audit.
The three current formulas on this page
Each mode comes from the same small family of electrical relationships. Ohm's Law gives I = V / R, the power equation gives I = P / V, and substituting power into Ohm's Law gives I = √(P / R).
Those formulas are appropriate for ideal resistive conditions. They are a fast way to estimate branch current, LED resistor current, or the amperage implied by a known load and supply voltage.
I = V / R
Use when supply voltage and load resistance are known.
I = P / V
Use when electrical power and circuit voltage are known.
I = √(P / R)
Use when power and resistance are known for an ideal resistive load.
Worked examples
For a 12 V supply and a 6 Ω load, the current is 2 A. That is the simplest Ohm's Law case and the same result the calculator shows in its default example.
For a 24 W device at 12 V, the current is also 2 A because I = P / V. The same current value can appear from different input pairs as long as the electrical relationship is consistent.
For a 36 W load across 9 Ω, the current is 2 A again. In this mode the calculator uses the square-root relationship, which is why the working equation shows the square root explicitly.
Why the current scale matters
A result in amps is correct, but not always the easiest way to judge the number. Small electronic circuits are often discussed in milliamps, while leakage and low-power measurement work may use microamps. Converting the same result into A, mA, and µA helps you see immediately whether you are in a power-electronics range, a bench-supply range, or a small-signal range.
That is why this current calculator shows the same electrical current at multiple unit scales. It reduces avoidable mistakes such as reading 0.002 A and forgetting that it is the same as 2 mA.
Why the same amps can imply different watts
Current alone does not tell the whole load story. Power depends on both current and voltage, which is why the same 2 A current can mean 10 W at 5 V, 24 W at 12 V, or 240 W at 120 V.
The comparison checkpoints on this page are there to stop a common interpretation mistake: treating amperage as if it directly described the whole electrical burden. A real current calculation should usually lead to a follow-on voltage, power, resistance, or component-rating check.
How to interpret the result safely
Current is often the number that determines whether a wire, fuse, resistor, or power supply is being pushed too hard. After solving amps, compare the result with component ratings, conductor limits, and thermal constraints rather than using the number in isolation.
If the result seems unusually high, check whether the voltage is realistic, whether the resistance is the actual load resistance under operating conditions, and whether the circuit is really a simple resistive case.
For bench work, use the current estimate to sanity-check a supply or resistor choice before you power the circuit. For anything safety-critical, confirm the calculation against the datasheet or a qualified design review.
When the estimate is rough
This calculator does not model AC phase angle, reactive loads, inrush current, temperature-dependent resistance, or non-linear devices such as semiconductors and motor drives.
If the load is not a simple resistor, treat the answer as a planning estimate and confirm the actual current with the appropriate AC, impedance, or device-specific method before relying on it.
Compare with related tools
Use this current calculator when you want amperes from one of the three common input pairs on this page. If you already know the voltage and resistance relationship directly, the answer is a straightforward Ohm's Law solve.
If you are working from different inputs, the related voltage, power, and Ohm's Law calculators are usually the faster path because they keep the formula aligned with the quantities you already know.
What is the difference between current and voltage?
Current is the flow of charge through the circuit, measured in amperes. Voltage is the electrical potential that pushes that flow. You need both values together to describe a circuit fully.
When should I use I = V / R instead of I = P / V?
Use I = V / R when you know the circuit voltage and resistance directly. Use I = P / V when you know the load wattage and voltage instead. Both are valid relationships, but the correct one depends on which two quantities are actually known.
What does the current result tell me?
The current result shows how much amperage the load draws under the assumptions of the selected formula. You can use it to compare with resistor ratings, fuse limits, power supplies, and wire-loading expectations.
Can I use this for AC circuits?
Only as a rough estimate for ideal resistive loads. Real AC analysis often requires impedance, power factor, and phase-angle treatment rather than simple DC-style resistance formulas.
Why does the calculator reject zero resistance or zero voltage in some modes?
Because those values would require division by zero in the selected formula. A zero divisor does not produce a valid finite current result in this simplified model.
Is current the same as amperage?
Yes. Current is the physical quantity and amperage is the way people usually refer to it in amps. In practical conversation, the two terms are used interchangeably.
How do I know which formula to use?
Start with the two quantities you already know. Voltage plus resistance uses Ohm's Law, power plus voltage uses the power equation, and power plus resistance uses the square-root relationship shown on this page.
How do I convert amps to milliamps or microamps?
Multiply amps by 1,000 to get milliamps and by 1,000,000 to get microamps. For example, 0.002 A is 2 mA and 2,000 µA. Showing the result in more than one unit helps prevent decimal-place mistakes.
Why can the same current mean very different power levels?
Because power depends on both voltage and current. A 2 A load at 5 V uses 10 W, but the same 2 A at 120 V represents 240 W. That is why amperage should be checked alongside voltage before making component or safety decisions.
When should I use an Ohm's law calculator instead?
Use an Ohm's law calculator when your problem is specifically centered on voltage, resistance, and current, or when you want to solve for one of those values in a broader circuit relationship.
