Hong Life CalculatorsUnderstanding the resistance converter — concept and principle
This converter changes an electrical resistance between ohms (Ω), milliohms (mΩ), micro-ohms (µΩ), kilohms (kΩ) and megohms (MΩ). You need it when a datasheet, a multimeter display and a parts list all use different prefixes: a pull-up resistor is written as 4.7 kΩ, a battery's internal resistance as 35 mΩ, an insulation test result as 200 MΩ, and a busbar joint as a few µΩ.
How it is calculated
Every unit is first turned into ohms, then divided by the size of the target unit: result = value × (ohms per "from" unit) ÷ (ohms per "to" unit). The factors are exact powers of ten: 1 MΩ = 10⁶ Ω, 1 kΩ = 10³ Ω, 1 mΩ = 10⁻³ Ω and 1 µΩ = 10⁻⁶ Ω. The calculator also lists your value in every other unit at once.
The principle
The ohm is the SI derived unit of resistance, defined by Ohm's law as one volt per ampere (1 Ω = 1 V/A). Prefixes such as kilo and milli are defined in the SI as exact decimal multipliers, so changing a prefix never changes the physical quantity; it only moves the decimal point by three places per step. Since the 2019 SI revision the ohm is realised in national laboratories through the quantum Hall effect, using the von Klitzing constant h/e² ≈ 25,812.807 Ω, but that does not affect the conversion factors, which remain exact.
Worked example
Default inputs: 1 kilohm converted to ohms.
- Convert the input to ohms: 1 kΩ × 1,000 Ω/kΩ = 1,000 Ω.
- Divide by the size of the target unit: 1,000 Ω ÷ 1 Ω = 1,000.
- Result: 1 kΩ = 1,000 Ω. The same value is also 0.001 MΩ, 1,000,000 mΩ and 1,000,000,000 µΩ.
How to read the result
Pick the prefix that leaves a number between about 1 and 999; that is how engineers write values. Typical ranges: copper wire and contacts are in the mΩ or µΩ range, most signal resistors sit between 10 Ω and 1 MΩ, and good insulation reads in hundreds of MΩ or more. A difference of one prefix is a factor of 1,000, so a misread prefix is never a small error.
Common mistakes
- Confusing m (milli, 10⁻³) with M (mega, 10⁶): the two differ by a factor of one billion.
- Typing "u" for µ and then misreading it later; µΩ is micro-ohms, one millionth of an ohm.
- Reading resistor codes such as 4k7 as 47 kΩ; 4k7 means 4.7 kΩ (the letter marks the decimal point).
- Forgetting that a component's tolerance (for example ±5 %) is far larger than any conversion rounding.
FAQ
Frequently asked questions
How many ohms are in a megohm?
One megohm is exactly 1,000,000 Ω, which is also 1,000 kΩ.
What does 0.47 kΩ equal in ohms?
Multiply by 1,000: 0.47 kΩ = 470 Ω.
Is milliohm the same as megohm?
No. A milliohm is 0.001 Ω, a megohm is 1,000,000 Ω; they differ by 10⁹.
Why does my multimeter show OL on the resistance range?
OL (overload) means the resistance is higher than the selected range can show, or the circuit is open; switch to a higher range.
Sources: BIPM, The International System of Units (SI Brochure), 9th edition, 2019 · NIST Special Publication 811 (2008), Guide for the Use of the International System of Units · IEC 60062, Marking codes for resistors and capacitors