Calculate output voltage from R1/R2 or design resistor values for a target voltage. Features load analysis, E24 nearest values, tolerance sensitivity, ratio visual, and common presets.
The voltage divider is one of the most fundamental circuits in electronics: two resistors in series produce an output voltage that is a fraction of the input. The output voltage is Vout = Vin × R2 / (R1 + R2), where R1 connects the input to the output node and R2 connects the output to ground. This simple relationship is used in sensor interfaces, biasing networks, level shifting, and signal attenuation.
However, the ideal voltage divider formula assumes no load — any current drawn from the output reduces the effective R2 and lowers the voltage. Understanding this load effect is critical in practical circuit design. The output impedance of a voltage divider is R1 ∥ R2, which sets a limit on how much current can be drawn before the voltage drops significantly.
This calculator works in two modes: calculate mode (given R1 and R2, find Vout) and design mode (given a target Vout, find R1 and R2 with E24 nearest standard values). Both modes include load analysis, tolerance sensitivity, and visual ratio display.
Designing a voltage divider often requires multiple iterations: calculate the ideal ratio, find standard resistor values, check the tolerance impact, and verify behavior under load. This calculator handles all steps in one tool, with automatic E24 value matching and a sensitivity table that shows how resistor tolerances affect the output.
Unloaded Divider: Vout = Vin × R2 / (R1 + R2) With Load: R2_eff = R2 ∥ R_load = R2 × R_load / (R2 + R_load) Vout = Vin × R2_eff / (R1 + R2_eff) Output Impedance: R_out = R1 ∥ R2 = R1 × R2 / (R1 + R2) Attenuation: dB = 20 × log₁₀(Vout / Vin) Design: R2 = R_total × (Vout / Vin) R1 = R_total − R2
Result: Vout = 5.00 V
With R1 = 14 kΩ and R2 = 10 kΩ: Vout = 12 × 10000 / (14000 + 10000) = 12 × 0.4167 = 5.00 V. The divider draws I = 12 / 24000 = 0.5 mA. Output impedance R_out = 14k ∥ 10k = 5.83 kΩ, meaning loads above ~58 kΩ will cause less than 10% voltage drop.
Many sensors (thermistors, photoresistors, strain gauges) are essentially variable resistors. Placing them in a voltage divider with a fixed resistor converts the resistance change to a voltage change that an ADC can read. The choice of fixed resistor value determines the sensitivity and linearity of the sensor interface — ideally, it should match the sensor's resistance at the midpoint of the measurement range.
At AC frequencies, reactive components (capacitors, inductors) form frequency-dependent voltage dividers. A capacitive divider passes high frequencies; an inductive divider passes low frequencies. The combination of resistive and reactive dividers creates filters — low-pass, high-pass, and band-pass — that are the building blocks of analog signal processing.
For applications requiring precise voltage ratios (DAC reference, ADC feedback networks), resistor networks with matched temperature coefficients are used. Integrated resistor dividers in a single package track each other thermally, maintaining ratio accuracy even as temperature changes. Thin-film resistor networks achieve ratio matching of 0.01% or better.
The load resistance appears in parallel with R2, reducing the effective bottom resistance. A lower R2_eff shifts the divider ratio, producing a lower output voltage. The effect is significant when R_load is within an order of magnitude of R2.
Generally no. A voltage divider has high output impedance and cannot supply significant current without voltage drop. For powering circuits, use a proper voltage regulator (LDO, buck converter). Voltage dividers are for biasing, measurement, and reference — not for power supply.
The E24 series defines 24 preferred resistor values per decade (1.0, 1.1, 1.2, ... 9.1), each available in multiples of powers of 10. They are spaced approximately 10% apart and cover the 5% tolerance range. Using E24 values ensures your resistors are readily available from suppliers.
With 5% resistors, the worst case is when R1 is 5% low and R2 is 5% high (or vice versa), causing the output to shift by roughly ±10% of the divider drop. The sensitivity table shows exact values for your specific configuration.
The same principle applies with capacitors: Vout = Vin × C1 / (C1 + C2). Note that the capacitor with the smaller value gets the larger voltage — opposite to resistive dividers. Capacitive dividers are used in AC coupling and charge-sharing circuits.
P_R1 = I² × R1 and P_R2 = I² × R2, where I = Vin / (R1 + R2). For most signal-level dividers, the power is milliwatts or less. Check that each resistor stays within its power rating (typically 1/8 W or 1/4 W for SMD/through-hole).