A voltage divider's output is Vout = Vin × R2 ÷ (R1 + R2), where R2 is the resistor between the output tap and ground. With 12 V across R1 = 1 kΩ and R2 = 2 kΩ, the output is 12 × 2 ÷ 3 = 8 V and 4 mA flows through the chain. A load across R2 lowers that figure.
Two resistors in series are the simplest way to derive a lower voltage from a higher one: scaling a 12 V signal into a 3.3 V ADC input, biasing a transistor base, or setting a regulator's feedback point. This calculator takes the supply voltage and both resistor values in kilohms and returns the tap voltage, the division ratio, the current through the chain and the power each resistor dissipates. Switch on the resistive load option to see how much a connected input drags the output down, since the load sits in parallel with R2. The working is shown line by line. One limit: it treats every part as an ideal resistor, so tolerance (1% or 5%), temperature drift and any reactive load are not modelled; a divider is also a poor power supply for anything drawing real current.
Type the voltage applied across the whole chain, Vin, in volts.
R1 runs from Vin to the output tap, R2 from the tap to ground. Both are in kilohms, so 470 Ω is 0.47.
Pick Resistive load and enter the input resistance of whatever the output feeds to see the loaded voltage.
Vout, ratio, current and resistor power update as you type, with a note if the load or dissipation is a problem.
Result Output voltage (Vout): 8
Division ratio Vout/Vin: 0.6667
Current through R1 (mA): 4
Power in R1 (mW): 16
Power in R2 (mW): 32
Unloaded Vout (V): 8
Two thirds of the total resistance sits below the tap, so the output is two thirds of 12 V: 8 V, with 4 mA flowing through both resistors.
Result Output voltage (Vout): 4.5
Division ratio Vout/Vin: 0.5
Current through R1 (mA): 0.45
Power in R1 (mW): 2.025
Power in R2 (mW): 2.025
Unloaded Vout (V): 4.5
Equal resistors split the supply in half, giving 4.5 V at 0.45 mA.
Result Output voltage (Vout): 3.3333
Division ratio Vout/Vin: 0.3333
Current through R1 (mA): 0.6667
Power in R1 (mW): 4.444
Power in R2 (mW): 1.111
Unloaded Vout (V): 5
The load in parallel with R2 makes 5 kΩ, so the output drops from 5 V to 3.33 V.
Vout = Vin × R2eff ÷ (R1 + R2eff), where R2eff = R2 × RL ÷ (R2 + RL) with a load, or R2 without
VinR1R2RLThe same current flows through R1 and R2, so by Kirchhoff's voltage law the supply splits in proportion to resistance. Current is Vin divided by the total resistance; with volts over kilohms the result is in milliamps. Power in each resistor is I² × R1 and Vout² ÷ R2, in milliwatts. A load adds a parallel path below the tap, lowering the effective bottom resistance and therefore the output.
R1 is connected between the input voltage and the output node; R2 is connected between the output node and ground. The output is taken across R2, so a larger R2 relative to R1 gives a higher output.
You need a ratio of 3.3 ÷ 5 = 0.66, so R2 ÷ (R1 + R2) = 0.66. A 1 kΩ R1 and 2 kΩ R2 gives 3.33 V, close enough for most logic inputs. Keep the total in the low kilohms for fast signals.
Whatever you connect, including a multimeter or an ADC pin, adds resistance in parallel with R2. If that load is not much larger than R2, the output sags. Select the resistive load option and enter the load's input resistance to see the effect.
A common rule of thumb is a load at least ten times R2, which keeps the error under about 10% of the unloaded voltage for a balanced divider. The tool warns when the drop exceeds 5%.
Yes. Current is Vin divided by R1 + R2, so doubling both halves the current and the dissipation. The trade-off is that higher values are more sensitive to loading and to noise pickup.
Compare the milliwatt figures with the part rating and leave margin. A common through-hole resistor is rated 250 mW and many 0603 surface-mount parts 100 mW; the tool flags dissipation above 250 mW.
Using this tool in an assignment, article or report? Copy a citation, or a link for your website.
Tools Directory Editorial Team. (2026, October 27). Voltage Divider Calculator. Tools Directory. Retrieved October 27, 2026, from https://tools.milunir.com/electronics-physics/resistors-and-capacitors/voltage-divider-calculator/
Tools Directory Editorial Team. “Voltage Divider Calculator.” Tools Directory, 27 Oct. 2026, https://tools.milunir.com/electronics-physics/resistors-and-capacitors/voltage-divider-calculator/. Accessed 27 Oct. 2026.
Tools Directory Editorial Team. “Voltage Divider Calculator.” Tools Directory. Last modified October 27, 2026. Accessed October 27, 2026. https://tools.milunir.com/electronics-physics/resistors-and-capacitors/voltage-divider-calculator/.
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