Voltage Divider Calculator
Output voltage, loading error and power of an R1/R2 divider — with E-series suggestions for your target ratio.
Rule of thumb: keep the divider current ≥ 10× the load current, or the output sags. For battery-powered designs the opposite pressure applies — a 10k/4.7k divider across a 12 V battery wastes 0.8 mA forever. Never use a plain divider as a power supply; it only sets reference voltages.
Voltage Divider Calculator computes the output of an R1/R2 resistive divider, with loading and power — free, instant and private in your browser. Anyone scaling voltages for ADCs, biasing transistors or making reference taps use it to skip the datasheet algebra: type your numbers, read the answer with the substituted formula shown step by step, and share an exact permalink of the calculation.
About Voltage Divider Calculator
Voltage Divider Calculator computes the output of an R1/R2 resistive divider, with loading and power using the standard engineering relation: Vout = Vin·R2/(R1+R2); loading error appears when the load resistance isn't ≫ R2. Worked live: 12 V across 10 kΩ + 4.7 kΩ taps out 3.84 V — close to a 3.3 V ADC's comfort zone. The result recalculates on every keystroke, the worked-example panel shows your numbers substituted into the formula, and the Copy permalink button encodes the inputs in the URL so a colleague opens exactly your calculation. Everything runs client-side — nothing you type leaves your device.
How to use Voltage Divider Calculator
- 1Enter your values — the tool starts with realistic defaults for this exact use case, so the worked example is meaningful immediately.
- 2Read the live result and the worked-example panel, which substitutes your numbers into the formula step by step.
- 3Adjust any input to compare scenarios, then use Copy result or Copy permalink to share the calculation.
Why use Voltage Divider Calculator?
- ✓Implements the real formula — Vout = Vin·R2/(R1+R2) — with the substitution shown, not a black box
- ✓Built for anyone scaling voltages for ADCs, biasing transistors or making reference taps
- ✓Copy result and permalink buttons — share the exact calculation in a README, forum answer or design review
- ✓100% free, no sign-up, runs entirely in your browser (works offline once loaded)
Frequently asked questions
How do you calculate voltage divider?+
The output of an R1/R2 resistive divider, with loading and power follows Vout = Vin·R2/(R1+R2); loading error appears when the load resistance isn't ≫ R2. For example, 12 V across 10 kΩ + 4.7 kΩ taps out 3.84 V — close to a 3.3 V ADC's comfort zone. The calculator applies the same relation and shows the substituted arithmetic so you can verify every step.
How do I pick divider resistor values, not just the ratio?+
Trade three pressures: low values waste current (12 V across 1 kΩ total burns 144 mW forever), high values pick up noise and get loaded by whatever you connect. 10 kΩ–100 kΩ total suits most sensing; go lower only when the load demands it.
Why does my divider's output sag when I connect the ADC?+
The ADC input (or its sample capacitor) parallels R2 and changes the ratio. Keep the divider's Thevenin resistance under ~10 kΩ for typical SAR ADCs, add a 100 nF at the pin, or buffer with an op-amp for high-impedance dividers.
Is the Voltage Divider Calculator free and private?+
Yes — completely free with no sign-up or usage limits, and it runs entirely in your browser: the values you enter are never uploaded or stored on a server.
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