Calculate the output voltage of a resistive divider and its loading effects.
The ideal divider ratio only holds with no load. Any load appears in parallel with R2 and pulls the output down, which is why divider resistances must be low compared with the load impedance. A divider feeding a low-impedance load needs either much lower resistor values or a buffer amplifier, and the output impedance figure tells you which.
Voltage Divider
V_out = V_in × R2 ÷ (R1 + R2); loaded output uses R2 in parallel with the load
V_out = V_in × R2 ÷ (R1 + R2); loaded output uses R2 in parallel with the load The ideal divider ratio only holds with no load. Any load appears in parallel with R2 and pulls the output down, which is why divider resistances must be low compared with the load impedance.
A divider feeding a low-impedance load needs either much lower resistor values or a buffer amplifier, and the output impedance figure tells you which.
This calculator takes 4 inputs: Input voltage, Upper resistor R1, Lower resistor R2, Load resistance across the output. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.