Tools you might need next
Decode resistor color bands to resistance value in ohms or find the correct color bands for a target resistance and tolerance.
Calculate current-limiting resistor value and wattage for LED circuits from supply voltage, forward voltage, and desired current.
Calculate output voltage and resistor values for voltage divider circuits from input voltage, R1, R2, and load considerations.
Voltage equals current times resistance in linear resistive circuits.
V = I × RPower is voltage times current and links to resistance.
P = V × I = I² × R = V² / RKnowing any two of V, I, R lets you find the third. Add P when power dissipation matters.
Updated: July 2026
Find power in a 330 Ω resistor at 20 mA before picking 1/4 W vs. 1/2 W.
Calculate current from 120 V and 900 W heater to choose branch protection.
See voltage across 10 Ω when supply is set to 2 A constant current.
Convert mA to A before using V = I × R.
Motors have reactive impedance and power factor. Use AC-specific analysis when needed.
Solve any two of voltage, current, resistance, and power to find the rest. Enter known values for quick circuit checks and component sizing.