How to use
- Choose two different quantities. Enter volts (V), amperes (A), ohms (Ω) or watts (W), as shown in the selected labels. Convert milliamperes to amperes first: 20 mA = 0.02 A.
- Press Calculate to display all four values and the circuit. Copy result copies the confirmed values. Any edit clears the result and diagram; Clear also empties the inputs.
Formula and interpretation
Ohm’s law is V = I × R; electrical power is P = V × I. All six pairs are supported: V/I, V/R, V/P, I/R, I/P and R/P. For example, voltage and power give I = P/V and R = V²/P. Values are nonnegative magnitudes for a passive resistor, not signed current directions.
Worked example
Choose voltage and resistance, then enter 12 V and 600 Ω. The current is 0.02 A (20 mA), and the resistor dissipates 0.24 W. Alternatively, enter 0.24 W and 600 Ω to recover the same operating point.
Limits and input errors
Inputs are between 0 and 10¹² in the selected base unit; resistance must be positive. Zero voltage, current or power with a known positive resistance gives zero for the other two. Without a known resistance, a zero pair is inconsistent or cannot uniquely determine resistance, so it is rejected. This is a steady DC model, excluding AC impedance and non-ohmic devices.
Positive numeric inputs below 10⁻¹⁰⁰ are rejected to avoid numerical underflow. Use a decimal point or comma without grouping; scientific notation such as 1e-6 is accepted.
Frequently asked questions
Why must the quantities be different?
Two readings of voltage alone cannot determine current or resistance. Select a different physical quantity, rather than entering another voltage measurement.
Is the power result a resistor rating?
No. It is calculated dissipation at this operating point. Tolerance, temperature and manufacturer derating are outside this calculation. Results are rounded only for display; very small values use scientific notation.