Voltage Divider Calculator

About the Voltage Divider Calculator

A voltage divider calculator computes the output voltage from two series resistors — one of the most fundamental circuits in all of electronics. The voltage divider splits an input voltage into a lower output voltage proportional to the resistor ratio: Vout = Vin × R2 / (R1 + R2). This deceptively simple circuit appears in thousands of applications: biasing transistors and op-amps, scaling sensor outputs to ADC input ranges, creating reference voltages, attenuating audio signals, providing logic level shifting between 5V and 3.3V systems, and implementing pull-up and pull-down networks. Our calculator goes beyond the basic output voltage to show current through the divider, power dissipated in each resistor (for component rating verification), the divider ratio, and the voltage drop across R1 — all the information needed to fully characterize a resistor divider circuit. It also shows the Thevenin equivalent of the divider (for load analysis) and warns when resistor power dissipation approaches standard component ratings. Used by electronics engineers, hobbyists, students, and technicians working with analog and digital circuits.

How It Works

Vout = Vin × R2 / (R1 + R2). Current: I = Vin / (R1 + R2). Voltage drop across R1 = Vin - Vout = I × R1. Power in R1: P_R1 = I² × R1. Power in R2: P_R2 = I² × R2. Total power: P_total = I² × (R1 + R2) = Vin × I = Vin² / (R1 + R2). Example 1 (5V to 3.3V level shifter): Vin = 5V, Vout = 3.3V. R2/(R1+R2) = 3.3/5 = 0.66. Choose R2 = 10kΩ: R1 = R2 × (Vin/Vout - 1) = 10,000 × (5/3.3 - 1) = 10,000 × 0.515 = 5,152Ω → use standard 5.1kΩ. Verification: Vout = 5 × 10,000/(5,100 + 10,000) = 5 × 0.662 = 3.31V. I = 5/15,100 = 0.331mA. Power: P_R1 = 0.000331² × 5,100 = 0.56mW; P_R2 = 0.000331² × 10,000 = 1.10mW — both well within ¼W resistor limits.

Tips & Best Practices

• ✓Load effect: connecting a load resistance R_L in parallel with R2 reduces effective R2 to R_eff = R2 × R_L / (R2 + R_L). For the output to remain accurate within 1%, R_L should be ≥ 100 × R2. If your load is a 10kΩ ADC input, use R2 ≤ 100Ω — or use an op-amp buffer after the divider to eliminate loading.
• ✓Resistor value selection: use the E24 or E96 standard resistor series for closest-tolerance values. Online resistor divider calculators help find E24/E96 pairs for exact ratios. For precision applications, use 1% metal film resistors; for non-critical biasing, 5% carbon film is adequate.
• ✓Temperature coefficient mismatch: if R1 and R2 have different temperature coefficients (tempcos), the divider ratio changes with temperature. For precision reference dividers, use matched-tempco resistor pairs or resistor networks designed for ratiometric stability.
• ✓AC voltage dividers: the same formula applies to AC voltages, but capacitive and inductive reactance creates frequency-dependent impedance. For audio or RF applications, account for parasitic capacitance — small capacitors in parallel with R2 create a low-pass filter, while inductance creates high-pass behavior.

Who Uses This Calculator

Electronics engineers designing sensor interface circuits that require voltage scaling to match ADC input ranges. Hobbyists and students building Arduino and Raspberry Pi circuits that connect 5V sensors to 3.3V logic inputs. Technicians calculating resistor networks for transistor and op-amp biasing circuits. RF and audio engineers designing attenuator networks and voltage reference circuits.