What is this Ohm's law tool used for?
This tool uses the basic relationship between voltage, current and resistance in an electrical circuit to solve the third variable from the two known values.
It is useful for quick checks in circuit design, resistor selection, fuse and cable sizing, and electronics hobby projects.
Formulas used
- V = I × R
- I = V / R
- R = V / I
Variables and meaning
- V
- Voltage, or electric potential difference across the circuit.
- I
- Electric current flowing through the circuit.
- R
- Resistance opposing the current in the circuit or component.
Unit reference tables
Voltage units
| Unit name | Symbol | SI equivalent | Typical use |
|---|---|---|---|
| Millivolt (mV) | mV | 0.001 V | Sensors and low-level signals |
| Volt (V) | V | 1 V | Base SI voltage unit |
| Kilovolt (kV) | kV | 1,000 V | High-voltage transmission |
Current units
| Unit name | Symbol | SI equivalent | Typical use |
|---|---|---|---|
| Milliampere (mA) | mA | 0.001 A | Electronic circuit currents |
| Ampere (A) | A | 1 A | Base SI current unit |
| Kiloampere (kA) | kA | 1,000 A | Industrial power systems |
Resistance units
| Unit name | Symbol | SI equivalent | Typical use |
|---|---|---|---|
| Ohm (Ω) | Ω | 1 Ω | Base SI resistance unit |
| Kiloohm (kΩ) | kΩ | 1,000 Ω | Electronic circuit resistors |
| Megaohm (MΩ) | MΩ | 1,000,000 Ω | Insulation-resistance measurements |
Worked examples
What voltage appears across a 10 Ω resistor at 2 A?
V = I × R = 2 A × 10 Ω = 20 V.
What current flows if a 12 V source is connected to 4 Ω?
I = V / R = 12 V / 4 Ω = 3 A.
Typical applications
- Circuit-board checks and resistor verification
- Current-limiting resistor sizing for LEDs and sensors
- Preliminary cable and fuse sizing checks
- Electronics education and hobby projects
Assumptions and limitations
- The formula applies to elements with approximately constant resistance; it is not directly valid for nonlinear devices such as diodes and transistors.
- Temperature-dependent resistance change is not included in this basic calculation.
- In reverse calculations, the denominator cannot be zero when solving for current or resistance.