Resistance Converter — ohm, milliohm, kilohm, megohm

The resistance converter above moves any resistance value between ohms and every prefix in common use, from microohms for busbar and contact resistance up to gigaohms for insulation testing. It also handles the electromagnetic abohm and electrostatic statohm found in older physics literature. Type a number, pick two units, and the result updates immediately, with the same quantity shown simultaneously in ohms, milliohms, kilohms and megohms.

Arb Digital maintains this as part of a free engineering converter library. Resistance spans a wider practical range than almost any other electrical quantity — a shunt resistor for current sensing might be 0.001 Ω while the insulation between two conductors in the same assembly is measured in hundreds of megaohms. Those two numbers appear on the same test report, and reading them without converting to a common unit makes comparison guesswork.

What This Resistance Converter Does

Resistance measures how strongly a material opposes the flow of electric current. The relationship is Ohm's law: the voltage across a conductor equals the current through it multiplied by its resistance. The SI unit is the ohm, symbol Ω, and it is formally defined as one volt per ampere. A component with one ohm of resistance drops one volt when one ampere flows through it.

The converter accepts values in any of nine units and returns any other. Because the SI prefixes are exact powers of ten, conversions among ohms, milliohms, kilohms, megohms and gigaohms involve no approximation whatsoever. The two CGS units are the only entries carrying a non-decimal factor, and both are included for reading historical sources rather than for daily work.

One naming detail catches people out. The unit formed from mega and ohm is conventionally written and pronounced megohm, dropping one vowel, while kilo and ohm stay separate as kilohm — though kilo-ohm is also seen. Both spellings refer to the same quantity, and this tool lists them the way they usually appear on datasheets.

How to Use It

1. Enter the resistance value you have, in whatever unit your meter or datasheet reports.
2. Choose the source unit from the first dropdown.
3. Choose the target unit from the second.
4. Read the headline result, which recalculates on every keystroke. The Convert button is retained for keyboard and screen-reader access.
5. Use Swap units to reverse the direction instantly, which is useful when checking a conversion in both directions.

The Formula: How Resistance Conversion Is Calculated

Every conversion pivots through the ohm. Your value is multiplied by the source factor to reach ohms, then divided by the destination factor:

result = value × factor(from) ÷ factor(to)

The prefix factors come straight from the BIPM SI Brochure and are exact: micro is 10⁻⁶, milli is 10⁻³, kilo is 10³, mega is 10⁶ and giga is 10⁹. The ohm itself is a coherent derived unit, expressible as kg·m²·s⁻³·A⁻².

The abohm equals exactly 10⁻⁹ Ω, which makes it identical in size to a nanoohm. The statohm equals approximately 8.987551787 × 10¹¹ Ω, the same speed-of-light-squared constant that appears in the stathenry — an unsurprising coincidence, since impedance in the electrostatic system inherits the same scaling. These factors follow NIST Special Publication 811, which is the authority used throughout this tool.

Reference Table: Every Supported Unit

Each factor is the number of ohms in one of that unit.

• ohm (Ω) — 1 (SI base for this quantity)
• microohm (µΩ) — 1 × 10⁻⁶ Ω
• milliohm (mΩ) — 1 × 10⁻³ Ω
• kilohm (kΩ) — 1 × 10³ Ω
• megohm (MΩ) — 1 × 10⁶ Ω
• gigaohm (GΩ) — 1 × 10⁹ Ω
• volt per ampere (V/A) — 1 Ω exactly; Ohm's law written as a unit
• abohm (abΩ) — 1 × 10⁻⁹ Ω
• statohm (statΩ) — 8.987551787 × 10¹¹ Ω

Reading Resistor Colour Codes and Letter Codes

Through-hole resistors carry colour bands where the first bands are significant figures and one band is a decimal multiplier. Surface-mount parts use printed digits with the same logic: a chip marked 472 is 47 followed by two zeros, or 4,700 Ω, which converts to 4.7 kΩ. A four-digit code such as 4701 means 470 followed by one zero, so 4,700 Ω again — the extra digit signals a tighter-tolerance series, not a different value.

Schematic notation uses a different trick. Rather than printing a decimal point that might vanish in a poor reproduction, designers put the multiplier letter where the point would go. So 4k7 is 4.7 kΩ, 2R2 is 2.2 Ω, 1M0 is exactly 1 MΩ, and 0R05 is 0.05 Ω. This convention is common in European and increasingly in international schematics, and it is worth recognising because a reader who mistakes 4k7 for 47 kΩ is off by a factor of ten in a way that often still produces a working-looking circuit.

Resistance Is Not Resistivity

These two are constantly confused and they are not interchangeable. Resistance is a property of a specific object — this particular length of this particular wire — and is measured in ohms. Resistivity is a property of the material itself, independent of shape, and is measured in ohm-metres. The link between them is geometry: resistance equals resistivity times length divided by cross-sectional area.

That means you cannot convert ohms to ohm-metres without knowing the dimensions of the conductor, and any tool claiming to do so directly is wrong. This converter deliberately handles resistance only. If you are working from a material property table, calculate the resistance for your specific geometry first, then bring that number here. The related quantity for cables is often quoted as ohms per kilometre, which is resistance per unit length — divide by the length in kilometres to get a plain resistance in ohms.

Very Small and Very Large Resistances Behave Differently

Measuring a milliohm-scale resistance with an ordinary two-wire multimeter is unreliable, because the resistance of the test leads themselves is often larger than the thing you are trying to measure. That is why four-wire Kelvin measurement exists: two leads carry the test current and two separate leads sense the voltage, so lead resistance drops out of the result. Any shunt, busbar, weld or contact-resistance figure quoted in microohms or milliohms almost certainly came from a four-wire measurement.

At the other extreme, insulation resistance in the gigaohm range is dominated by surface contamination and humidity rather than the bulk material. A cable that measures 500 MΩ on a damp morning may measure several gigaohms after drying. Insulation test results are therefore always quoted with a test voltage and often a temperature, because the number alone means little. When converting these figures, keep the test conditions attached to them — the conversion is exact, but the underlying measurement is conditional.

Where Resistance Fits With the Other Electrical Units

Resistance, capacitance and inductance together determine how a circuit responds over time and frequency. An RC time constant is resistance times capacitance in ohms and farads; use the capacitance converter for the farad side. An RL time constant is inductance divided by resistance, in henries and ohms — see the inductance converter. Power dissipated in a resistor is current squared times resistance, which lands you in watts and the power converter, and the energy that accumulates over time belongs to the energy converter.

Conductance, the reciprocal of resistance measured in siemens, is a separate quantity with its own unit and is not offered here for the same reason resistivity is not: mixing reciprocal quantities into one unit list is the fastest way to produce a silently wrong answer. When a datasheet quotes siemens, invert it to get ohms before using this tool.

Temperature Changes Resistance, and the Coefficient Tells You How Much

Metallic conductors get more resistive as they warm. Copper's resistance rises by roughly four tenths of a percent per degree Celsius, which sounds small until you consider a motor winding running fifty degrees above ambient: its resistance is about twenty percent higher hot than cold. Any winding resistance figure quoted without a temperature is therefore incomplete, and standards for motor and transformer testing require the measurement temperature to be recorded alongside the value.

Resistors made for precision work fight this with alloys chosen for a low temperature coefficient, quoted in parts per million per degree. A 25 ppm/°C resistor drifts 0.0025 percent per degree, so a thirty-degree swing moves it less than a tenth of a percent. Ordinary thick-film chip resistors are often specified at 100 ppm/°C or worse, which matters in any circuit setting a reference or a gain. Converting units does not touch this: 4.7 kΩ converts to 4,700 Ω exactly, but the physical part may sit anywhere inside its tolerance and temperature band.

Semiconductors behave in the opposite direction. Thermistors are built to exploit that, with negative temperature coefficient types dropping sharply in resistance as they heat, which is why an NTC thermistor works as both an inrush limiter and a temperature sensor. When a thermistor datasheet quotes a resistance at 25 °C, that reference temperature is part of the specification, not decoration.

Standard Resistor Values and the E-Series

Resistors are not made in arbitrary values. They follow the E-series, a set of preferred numbers spaced logarithmically so that consecutive values differ by roughly a fixed percentage. The E12 series gives twelve values per decade, spaced about twenty percent apart, which is why 4.7 kΩ, 5.6 kΩ and 6.8 kΩ exist while 5 kΩ generally does not. E24 doubles the density, and E96 gives ninety-six values per decade for one percent parts.

The spacing is chosen so that the tolerance bands of adjacent values just about touch, meaning every possible resistance is covered without manufacturing redundant parts. The practical consequence for anyone converting values is that a calculation returning 5,000 Ω should be rounded to a real E-series value before it becomes a purchase order. Converting 5 kΩ to 5,000 Ω is arithmetically fine and commercially useless if the series you are buying from jumps from 4.7 kΩ to 5.6 kΩ. Check the value exists before you specify it.

Common Mistakes to Avoid

• Misreading 4k7 as 47 kΩ — the letter is the decimal point, so 4k7 is 4.7 kΩ.
• Converting ohms to ohm-metres — that is resistivity, and it requires the conductor's length and cross-section.
• Trusting a two-wire measurement below about an ohm, where lead resistance dominates the reading.
• Mixing kilohms and farads in a time constant instead of converting both to base SI units first.
• Treating siemens as a resistance unit — conductance is the reciprocal quantity and must be inverted first.

Related Free Tools From Arb Digital

Combine this with the capacitance converter and the inductance converter for full RLC work, the electric charge converter for coulombs and amp-hours, and the power converter for dissipation figures in watts. The energy converter covers joules and kilowatt-hours. Every converter we publish is listed in the free online tools hub.

Frequently Asked Questions