Voltage Divider Calculator

Use Vout = Vin × R2 / (R1 + R2). The output across R2 is the fraction R2/(R1+R2) of the input voltage. A 12 V supply with two 10 kΩ resistors gives 6 V at the midpoint.

Pick R1 first (a common value like 10 kΩ), then solve for R2 = R1 × Vout / (Vin − Vout). For 3 V from 12 V with R1 = 10 kΩ, R2 = 10 kΩ × 3 / 9 ≈ 3.33 kΩ — use the nearest standard value.

No — a divider made of resistors can only step voltage down. Vout is always between 0 and Vin. To step voltage up you need a transformer (AC) or a boost converter (DC).

Yes — the load draws current in parallel with R2, which lowers the effective R2 and drops Vout. Keep the divider current at least 10× the load current (the “bleeder rule”) so the loading error stays small.

The divider current is I = Vin / (R1 + R2), and each resistor dissipates I²R watts. Choose resistors rated for at least twice the actual dissipation — a 2× safety margin keeps them cool.