Voltage Divider Calculator

Solve for any single unknown from the classic divider equation Vout = Vin × R2 ÷ (R1 + R2). Enter Vin and both resistors to get Vout, or provide Vin, Vout, and one resistor to solve for the other. Also returns the divider ratio K = Vout / Vin = R2 ÷ (R1 + R2) and the series current I = Vin ÷ (R1 + R2).

Add an optional load resistor RL in parallel with R2 and get the true loaded output. The app computes the effective lower resistance REQ = R2 × RL ÷ (R2 + RL), then Vout = Vin × REQ ÷ (R1 + REQ). It also reports the Thevenin equivalent RTH = R1 ∥ R2 and a load-error percentage, so you can see exactly how much the output droops.

Check power dissipation on each resistor before you build: P_R1 = I² × R1 and P_R2 = I² × R2, or equivalently V_R1² ÷ R1 and V_R2² ÷ R2. The app flags when a standard 1/4 W, 1/2 W, or 1 W resistor is undersized, and reports total divider current so you can balance stiffness against quiescent power draw in battery-powered designs.

Enter a desired Vout and Vin, and the app suggests R1/R2 pairs from the E12 and E24 standard resistor series, plus the nearest preferred values. Also supports the simplification shortcuts: if R1 = R2, Vout is exactly half of Vin; if R2 ≫ R1, Vout approaches Vin; if R2 ≪ R1, Vout approaches 0 V.

Generate a clean bill of materials with resistor values, power ratings, tolerance, and quantities. Export a PDF design summary or CSV for your lab notebook, procurement list, or teaching handout. All calculations and reports stay on the device and work fully offline.

Enter resistance in ohms, kilohms, megohms, or milliohms, and voltage in millivolts, volts, or kilovolts. The app normalizes every input, shows all intermediate values in consistent units, and converts instantly between ranges. No unit-conversion mistakes in lab work or production documentation.