Robert Eisele
Systems Engineer, Architect and DBA

Voltage Divider Calculator

A voltage divider lets you convert an input voltage to a lower output voltage. For example a 5V input can be converted to a 3V3 output quite easily. The basic setup is made of two resistors:

But choosing the right resistors is quite tricky. You could take the formula and try some values in order to approximate the values or use the calculator formula:

Input VoltageV
Output VoltageV

Possible resistor values for input voltage of 5V and output voltage of 3.3V, ordered by error:
R1R2ActualErrorPower Disipation
330Ω680Ω3.366V0.066V0.025W
47Ω100Ω3.401V0.101V0.170W
47kΩ100kΩ3.401V0.101V0.000W
4.7kΩ10kΩ3.401V0.101V0.002W
470Ω1kΩ3.401V0.101V0.017W
4.7Ω10Ω3.401V0.101V1.701W
220Ω470Ω3.406V0.106V0.036W
22kΩ47kΩ3.406V0.106V0.000W
2.2kΩ4.7kΩ3.406V0.106V0.004W
10kΩ22kΩ3.438V0.138V0.001W
100Ω220Ω3.438V0.138V0.078W
1kΩ2.2kΩ3.438V0.138V0.008W
220Ω330Ω3.000V0.300V0.045W
2.2kΩ3.3kΩ3.000V0.300V0.005W

Please note: Don't use a voltage divider for high voltages, as the entire current has to pass the resistors, which will hurt them a lot. Alternatives are voltage regulators! And even more important: You shouldn't use low value resistors in real world voltage deviders. The power disipation column states how much energy is converted into heat.