Voltage divider calculator
Solve for Vout, or start from the Vout you want and get the best standard resistor pairs, from E6 to E192 or from the parts in your drawer, with the error, the current they burn, the effect of a load and the range they will really give you at your tolerance.
Best standard pairs
Pairs of standard resistor values (the E-series) that come closest to your target Vout, closest first. Click a column heading to sort by it.
The formula
Vout = Vin · R2 / (R1 + R2) I = Vin / (R1 + R2) With a load: use R2 ∥ RL = R2 · RL / (R2 + RL) in place of R2
When to use it
A resistive divider is the right tool for sensing a voltage — battery monitoring on an ADC pin, a feedback node, a logic-level reference that draws next to nothing. It is the wrong tool for powering anything: the output moves with the load, and the resistors dissipate the full divider current all the time. If the load current is not far below the divider current, use a regulator.
Pitfalls
- Tolerance stacks: two 5 % resistors can move Vout by about ±5 % when Vout is half of Vin, and by up to ±10 % when it is a small fraction of Vin, which is why the table shows the real range, not just the nominal value.
- A load in parallel with R2 lowers Vout. Enter it and the table recomputes; the rule of thumb is a divider current at least ten times the load current.
- High-value dividers (megohms) save battery but feed an ADC slowly: check the ADC’s input impedance or add a capacitor across R2.
- Without a load, the same ratio in a different decade gives the same Vout; set the current or total resistance range to pick the decade you can afford. With a load, each decade gives a different Vout, so the table lists them separately.
Need the whole board designed, not just the divider?