Ohm's Law
Enter 2 values, the third will be locked and calculated.
to instantly get the third value.
Ohm's Law Calculator
⚡ Formula of Ohm's law in simple words
Ohm's Law is the basis of all electrical engineering. It relates the three main parameters of the circuit: Voltage (V), Current Strength (I) and Resistance (R).
Basic formula: V = I · R
To find one parameter, you need to know the other two:
- Looking for Voltage (V):
I · R(Current multiplied by Resistance) - Looking for Current (I):
V / R(Voltage divided by Resistance) - Looking for Resistance (R):
V / I(Voltage divided by Current)
💡 Connection with power (Watts)
Often, together with Ohm's law, you need to calculate power (P) to understand whether the wiring or device will burn out.
Formula: P = V · I.
If you are calculating the costs of operating appliances, we recommend our calculator electricity costs.
Examples of calculations from life
Example 1: Selecting a resistor for an LED
You have a 12V source, but the LED needs 2V and a current of 0.02A. We need to pay off the extra 10V.
Calculation R: 10V / 0.02A = 500 Ohm.
For accurate selection of parts, use the table color marking of resistors.
Example 2: How much current does the device consume?
The heater has a resistance of 24 Ohms and is plugged into a 220V outlet.
Calculation I: 220V / 24 Ohm ≈ 9.16 Ampere.
Reference table of resistances
Values may vary, but you can use these as a rough estimate:
| Object | Resistance (Ω) |
|---|---|
| Copper wire (1m, 1mm²) | ~0.0175 Ω |
| Incandescent lamp (60W) | ~880 Ω (hot) |
| Human body (dry) | 100,000 - 500,000 Ω |
Frequently asked questions (FAQ)
🔹 Why doesn’t the calculator count if you enter 3 values?
Ohm's Law works on the principle: “You know two, find the third.” If you enter all three parameters, no calculation is required. Just leave the field you want to search blank.
🔹 Is it possible to enter fractional numbers?
Yes, of course. Use a period or comma (for example, 0.5 or 1.2). If you are not sure how to write fractions correctly, read our help: what is a decimal.
🔹 Does this work for alternating current (AC)?
For simple heaters (iron, kettle, light bulb) - yes. For motors and transformers, the calculation will be inaccurate, since there appears reactance (impedance), which this calculator does not take into account.
🔹 What is Ohm's Triangle?
This is a visual cheat sheet. Imagine a triangle divided into three parts. V at the top, I and R at the bottom. Cover what you are looking for with your finger and you will see the formula. For example, if you closed V, you see I and R side by side (which means we’re multiplying).