Electric Resistance Converter
Convert electric resistance units — ohms, kilohms, megaohms, milliohms, and more. Free online resistance converter for circuit design, electronics, and electrical engineering.
Understanding Electric Resistance
Electric resistance measures how much a material opposes the flow of electric current. You express resistance in ohms (Ω), named after German physicist Georg Ohm.
Resistance depends on material properties, length, cross-sectional area, and temperature. Conductors like copper have low resistance. Insulators like rubber have extremely high resistance.
Resistance Formulas and Ohm's Law
R = V / I
Ohm's Law: Resistance equals voltage divided by current. This fundamental relationship defines resistance in DC circuits.
R = ρ × L / A
Resistivity formula: Resistance equals resistivity times length divided by cross-sectional area. Use this for conductor sizing.
P = I² × R
Power dissipation: Power equals current squared times resistance. This determines resistor wattage requirements.
Example: A copper wire 100 meters long with 1 mm² cross-section has R = 1.68 × 10⁻⁸ Ω·m × 100 m / 1 × 10⁻⁶ m² = 1.68 ohms.
Common Resistance Conversions
| Ohms (Ω) | Milliohms (mΩ) | Kilohms (kΩ) | Megaohms (MΩ) |
|---|---|---|---|
| 0.001 | 1 | 0.000001 | 1 × 10⁻⁹ |
| 0.01 | 10 | 0.00001 | 1 × 10⁻⁸ |
| 0.1 | 100 | 0.0001 | 1 × 10⁻⁷ |
| 1 | 1,000 | 0.001 | 1 × 10⁻⁶ |
| 1,000 | 1,000,000 | 1 | 0.001 |
| 1,000,000 | 1 × 10⁹ | 1,000 | 1 |
Wire Gauge and Resistance Reference
| AWG | Diameter (mm) | Resistance per 1000m (Ω) | Max Current (A) |
|---|---|---|---|
| 10 | 2.59 | 3.28 | 30 |
| 12 | 2.05 | 5.21 | 20 |
| 14 | 1.63 | 8.29 | 15 |
| 16 | 1.29 | 13.2 | 10 |
| 18 | 1.02 | 21.0 | 7 |
| 20 | 0.81 | 33.3 | 5 |
Practical Applications
Resistor Selection
Standard resistor values follow E-series preferences. E12 series provides 12 values per decade: 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82 ohms.
Circuit Protection
Fuses and circuit breakers protect against overcurrent. A 15-amp breaker trips when current exceeds 15 amperes, preventing wire overheating.
Heating Elements
Electric heaters use high-resistance nichrome wire. A 1500-watt heater at 120 volts uses R = V²/P = 120²/1500 = 9.6 ohms of resistance.
Insulation Testing
Megohmmeters measure insulation resistance in megaohms. Good insulation shows values above 100 MΩ. Values below 1 MΩ indicate deteriorated insulation.
Frequently Asked Questions
How does temperature affect resistance?
Most conductors increase resistance with temperature. Copper resistance increases about 0.4 percent per degree Celsius. Semiconductors decrease resistance as temperature rises.
What is the difference between resistance and resistivity?
Resistivity is a material property measured in ohm-meters. Resistance depends on resistivity plus the object's dimensions. Resistivity describes the material. Resistance describes a specific component.
Why do resistors have color bands?
Color codes indicate resistance value and tolerance. A 4-band resistor uses two digit bands, one multiplier band, and one tolerance band for quick identification.
How do you measure resistance?
Use an ohmmeter or multimeter on the resistance range. Disconnect power and isolate the component from the circuit for accurate measurements.
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