Electrical Resistance Converter

Resistance measures how strongly a material opposes the flow of electric current. The SI unit is the ohm (Ω), named after Georg Ohm. Put one volt across one ohm and exactly one ampere flows, which is Ohm’s law in its plainest form.

Metric prefixes:

• 1 Ω = 1,000 mΩ (milliohms)
• 1 kΩ = 1,000 Ω (kilohms)
• 1 MΩ = 1,000,000 Ω (megohms)
• 1 GΩ = 1,000,000,000 Ω (gigohms)

Ohm’s law:

• Resistance = Voltage ÷ Current (R = V / I)
• Current = Voltage ÷ Resistance (I = V / R)
• Power = Voltage × Current (P = V × I)

Enter a voltage in the optional field above and the page runs those last two for you. The power line is the one people forget: a 100 Ω resistor across 12 volts passes 120 mA and burns 1.44 watts, which will destroy the quarter-watt part most beginners reach for. Rule of thumb, pick a resistor rated at roughly double the calculated dissipation.

For scale:

• A metre of 1 mm² copper wire: about 0.017 Ω
• A typical resistor: 100 Ω to 10 kΩ
• Wet human skin: 1–10 kΩ
• Dry human skin: 100 kΩ to 1 MΩ
• A good insulator: 1 GΩ and up

That skin figure is why voltage matters so much for safety. Dry skin’s high resistance limits the current a low voltage can drive through you, but wet skin can fall by two orders of magnitude, and the same voltage then pushes far more current.

For working out the resistance of an actual cable run, this converter is the wrong tool: that depends on conductor material, cross-section and length, and the voltage drop calculator and the wire gauge converter handle it properly.

One distinction trips up anyone moving from DC to AC: resistance is not impedance. Resistance applies to steady direct current. In an AC circuit, capacitors and inductors add a frequency-dependent opposition called reactance, and the combination is impedance, also measured in ohms. A part can have almost zero resistance yet a large impedance at the right frequency, which is the whole basis of how filters and tuned circuits work.