The result assumes nothing else draws current from the output. A load in parallel with R2 lowers Vout, so keep the load resistance much larger than R2 or use a regulator.
Ohm's law formulas
| To find | From V and I | From V and R | From I and R | From P and V | From P and I | From P and R |
|---|---|---|---|---|---|---|
| Voltage V | — | — | I × R | — | P ÷ I | √(P × R) |
| Current I | — | V ÷ R | — | P ÷ V | — | √(P ÷ R) |
| Resistance R | V ÷ I | — | — | V² ÷ P | P ÷ I² | — |
| Power P | V × I | V² ÷ R | I² × R | — | — | — |
Unit prefixes
| Prefix | Factor | Example |
|---|---|---|
| µ (micro) | 0.000001 | 250 µA = 0.00025 A |
| m (milli) | 0.001 | 20 mA = 0.02 A |
| k (kilo) | 1,000 | 4.7 kΩ = 4,700 Ω |
| M (mega) | 1,000,000 | 1 MΩ = 1,000,000 Ω |
Standard resistor values (E24, 5%)
1.0, 1.1, 1.2, 1.3, 1.5, 1.6, 1.8, 2.0, 2.2, 2.4, 2.7, 3.0, 3.3, 3.6, 3.9, 4.3, 4.7, 5.1, 5.6, 6.2, 6.8, 7.5, 8.2, 9.1, and the same values × 10, × 100, × 1k and so on. The voltage divider tab suggests the nearest E24 value from the IEC 60063 series.
OhmCalc assumes ideal components and DC (or resistive AC) circuits. For AC loads with a power factor, real power is V × I × PF. Mains voltage can kill: these tools are for learning and low-voltage design.
Frequently asked questions
How do I get 5 V from 12 V with a divider?
With R1 = 10 kΩ, R2 = 7.14 kΩ; the nearest E24 value is 7.5 kΩ, which gives about 5.14 V unloaded.
Can a voltage divider power a device?
Only very light loads. For anything drawing real current, use a voltage regulator or buck converter.
What is a voltage divider used for?
Scaling a voltage down for an analog input, biasing transistors and setting reference levels.
Is OhmCalc free?
Yes, with no sign-up or ads.
Are my values saved?
Yes, in this browser only.