Physics Tools
What It Does
Works out any two of voltage, current, resistance, and power from the other two, using Ohm’s law and the power formulas — and shows which formula it used. Everything runs in your browser.
How to Use It
- Enter exactly two of V, I, R, P (leave the other two blank).
- Read the two computed values and the formula used for each.
- Use SI prefixes (
k,m, …) freely — e.g.4.7kfor 4.7 kΩ. - Click Copy on any computed value.
R = 0, a short circuit that makes the current undefined.About Ohm’s Law & the Power Wheel
Ohm’s law states that the current through a resistor is proportional to the voltage across it and inversely proportional to its resistance — V = I·R. Combined with the definition of electrical power, P = V·I, these give a “wheel” of twelve equivalent formulas relating voltage, current, resistance, and power, so any two of them determine the other two. That is why you can find the power a resistor dissipates from just its resistance and the current (P = I²R), or the resistance you need from a target power and supply voltage (R = V²/P).
Example
V = 12 V and R = 4 Ω → I = V / R = 3 A and P = V·I = 36 W.
Frequently Asked Questions
How many values do I need to enter?
Exactly two. The wheel has a formula for every pair of quantities, so any two of voltage, current, resistance, and power determine the remaining two.
What happens when resistance is zero?
A resistance of zero is a short circuit, and the predicted current becomes infinite. Real supplies can’t deliver that, so the tool flags the combination instead of showing a nonsensical number.
Does Ohm’s law always apply?
It holds for ohmic components such as ordinary resistors. Devices like diodes and filament bulbs are non-ohmic — their resistance changes with voltage, current, or temperature.
Is my data sent to a server?
No. Every calculation runs locally in your browser; nothing you enter is transmitted or stored.