Voltage divider calculator

Formula

How it works

Two resistors in series share the input voltage in proportion to their resistance; the output is taken across R2. Connecting a load to the output changes the result.

Worked example

The same calculation with the default values:

• Input voltage 12 V
• Resistor R1 (top) 10,000 Ω
• Resistor R2 (bottom) 4,700 Ω

1. Vout = 12 × 4,700 ÷ (10,000 + 4,700) = 3.836735 V
2. I = 12 ÷ (10,000 + 4,700) = 0.000816 A
3. P = 12 × 0.000816 = 0.009796 W

Result: Output voltage: 3.83673469 V · Current (milliamperes): 0.81632653 mA · Total power: 0.00979592 W

Common mistakes

• Forgetting that this ideal formula assumes no current is drawn from the output (an unloaded divider) - connecting a real load in parallel with R2 changes the effective resistance and lowers Vout below the calculated value.
• Mixing up R1 and R2 - swapping them flips which fraction of the input voltage appears at the output.
• Using a voltage divider as a power supply for a circuit needing significant current - dividers are efficient for signal-level sensing but waste substantial power and sag badly under real current draw, unlike a regulated supply.