LIBRARYOhm's law.

What Ohm's law is, how to rearrange V = I x R for voltage, current, or resistance, and the power it sets. With a live calculator and a worked board example.

Ohm's law relates voltage, current, and resistance in one equation. Rearranged, it gives you current or resistance, and the power follows. Know any two and you have the rest. Georg Ohm published the relationship in 1827, and it holds for the resistive parts on every board here.

Fig 1

V = I \cdot R

Inputs

Solve for

VoltageVThe voltage across the component (e.g. 3.3 V or 5 V).ResistanceΩThe resistance, in ohms.

Result

10.0

mA · current

V = I × R, rearranged. Power is V × I.

Power dissipated

33 mW

Solve for voltage, current, or resistance, and read the power. ↗

The three forms

They are one equation, written for whatever you are missing. Know the current and the resistance and you want the voltage. Know the voltage and the resistance and you want the current. Know the voltage and the current and you want the resistance. Keep the units honest, volts and amps and ohms, and the arithmetic is exact.

I = \frac{V}{R} \qquad R = \frac{V}{I} \qquad P = V \cdot I

Why it matters

Almost every small design decision is an Ohm's-law step. Sizing a pull-up resistor on a One Thousand Drones L1.01 board is one: the resistor sits between the 3.3 V rail and a signal pin, and its value sets how much current flows when the pin pulls low. Pick the resistance and Ohm's law tells you the current; pick a target current and it tells you the resistance.

Checkpoint

Quick check

Ohm's law says voltage equals what?

To find the current when you know the voltage and resistance, you divide what by what?

The power a simple resistive part uses is which of these?

0 / 3 correctSign in to log XP

Prerequisite: voltage, current, and resistance

Calculate it: the Ohm's law calculator

Next: power and heat

One Thousand Drones engineering team · verified 2026-07

Want the whole Fundamentals cluster as one book?

▸ Sign in to suggest an improvement