Circuits and conductors
Voltage divider
- where
- voltage across R₂ (V)
- supply voltage (V)
- divider resistances (Ω)
Explain this equation
Works out the voltage across R₂ when two resistances are in series across a supply. Used for sensing circuits, reference voltages and checking how a supply splits.
V₂ is the voltage across R₂. Vₛ is the supply voltage across both. R₁ and R₂ are the two series resistances.
Both resistances carry the same current, so voltage shares in proportion to resistance. R₂/(R₁ + R₂) is R₂’s share of the total, and that share of the supply appears across it.
Sense check: 12 V across 10 Ω and 20 Ω gives 8 V across R₂. Equal resistances split the supply in half.
Watch out: anything connected across R₂ forms a parallel path and lowers the voltage. This is the unloaded figure.
Series resistors share voltage in proportion to their resistance. Find the fraction of total resistance represented by R₂ and multiply by supply voltage.
Attaching a load across R₂ changes the effective resistance. Recalculate the parallel combination before applying this formula.
Enter your values to see the result.
Common mistake
Ignoring loading by another component.
Limits
Unloaded divider and ideal voltage source.
Sources
The tools calculate the displayed equation. They do not automatically choose cable sizes, approve installations, supply current regulatory tables, certify equipment or replace inspection and testing.