Potential Divider Calculator
Calculate resistor divider output voltage, input voltage, resistor values, current, power, and the closest preferred E-series pair.
About potential dividers
Vout = Vin × R2 / (R1 + R2)
I_divider = Vin / (R1 + R2)
A resistor divider suits low-current references and measurement inputs. If a load is connected to Vout, its resistance sits in parallel with R2 and pulls the output below the ideal value — keep the divider current well above the load current, or buffer the output.
Preferred (E-series) resistors
Real resistors come in standardised E-series values (E6, E12, E24…). The calculator searches the chosen series for the pair whose output is closest to your target, and reports the resulting error.
Worked example: 9 V down to 3.3 V
To scale a 9 V input toward a 3.3 V rail, enter 9 V in and 3.3 V out: the closest standard E24 pair is 47 kΩ on top and 27 kΩ on the bottom, which outputs 3.28 V — a −0.5% error. Remember a divider only holds that voltage under light load; draw real current from the tap and it sags.
Loading changes the answer
The formula assumes nothing is drawn from the output, which is only true when whatever you connect has a very high input impedance. Attach a load comparable to the lower resistor and it appears in parallel with it, pulling the output voltage below the calculated value. The usual rule is to keep the divider's resistance well below the load's — a factor of ten is the common guideline — but that trades against current wasted in the divider itself, which matters onbattery-powered designs.