Electrical Resistance Converter

How to use this calculator

Resistance value — Type the number. Decimals work. So do large integers: 470078 Ω converts cleanly to 0.470078 MΩ (that’s in the screenshot at the top of this page, and yes, the calculator handles it).

From unit — The unit your value is currently in.

To unit — The unit you want.

The converted result shows large in the output panel, with four reference values underneath it simultaneously: ohms, kilohms, megaohms, and conductance in millisiemens. You get all of them from one input, which matters when you’re cross-checking a schematic that mixes units across components.

The conversion formula

Like voltage, resistance units are all metric and all powers of 1,000. The ohm is the base unit.

1 kilohm = 1,000 ohms 1 megaohm = 1,000 kilohms = 1,000,000 ohms 1 milliohm = 0.001 ohms

To go from kΩ to MΩ: divide by 1,000. From Ω to kΩ: divide by 1,000. From MΩ to Ω: multiply by 1,000,000.

The milliohm sits on the other side of zero. 1 mΩ is 0.001 Ω. To convert mΩ to Ω, divide by 1,000. To convert Ω to mΩ, multiply by 1,000.

Conductance is different: it’s the reciprocal of resistance. 1 siemens = 1 / 1 ohm. So a 470 kΩ resistor has a conductance of 1 / 470,000 = 0.00000213 S, or 2.13 µS. The converter calculates this for you; you don’t need to run the reciprocal yourself.

Full unit reference table

In practice, most resistors you’ll place on a PCB are in the 1 Ω to 10 MΩ range. Below that (milliohm territory) you’re dealing with things like current sense resistors, motor winding resistance, and connector contact resistance. Above 10 MΩ, you’re typically measuring insulation quality rather than a discrete component.

Common conversions at a glance

The pair you’ll use most often: kilohms to ohms (×1,000) and ohms to kilohms (÷1,000). Most schematic software and datasheets mix these two freely, and checking that a 4.7 kΩ resistor in a schematic matches the 4,700 Ω value in a calculation is a routine sanity check.

Resistor color codes: where unit reading gets annoying

Physical resistors don’t have their values printed on them in text. They use color bands. 4 bands for standard resistors, 5 bands for precision resistors. Each color maps to a digit or multiplier, and the multiplier is where the unit conversion lives.

For a 4-band resistor:

• Band 1: first digit
• Band 2: second digit
• Band 3: multiplier (power of 10)
• Band 4: tolerance

The multiplier band tells you how many zeros to add. Gold means ×0.1, silver means ×0.01, brown means ×10, red means ×100, and so on up through white (×1,000,000,000).

A resistor with bands Orange, Orange, Orange, Gold is 33 × 10³ Ω = 33,000 Ω = 33 kΩ, with ±5% tolerance (gold band).

A resistor with bands Yellow, Violet, Yellow, Gold is 47 × 10⁴ Ω = 470,000 Ω = 470 kΩ.

The color code gives you ohms directly. The converter then handles whatever unit your schematic or BOM uses. If your BOM lists values in kΩ and your color code calculation gives you ohms, one division by 1,000 and you’re done.

Real-world examples

Voltage divider design

You’re building a voltage divider to step down 5V to 3.3V for an ADC input. The formula for the output voltage is:

Vout = Vin × R2 / (R1 + R2)

A common choice: R1 = 10 kΩ, R2 = 22 kΩ gives you 5 × 22 / (10 + 22) = 3.4375V. Close enough.

Insulation resistance testing

An electrician tests the insulation resistance of a cable before connecting it to a 230V AC supply. The meter reads 450 MΩ.

The rule of thumb for insulation resistance: at least 1 MΩ for most building wiring, though in practice anything below 100 MΩ on a new installation warrants investigation. Safety standards for specific applications can require 1,000 MΩ or higher.

Current sense resistor

A power supply designer is using a 50 mΩ shunt resistor to measure current. At 10A of load current, what’s the voltage drop across the shunt?

Pull-up resistor for an I2C bus

An I2C bus needs pull-up resistors on both the SDA and SCL lines. A common value for 400 kHz fast-mode operation is 2.2 kΩ.

RF input impedance

A radio receiver has an input impedance of 50 Ω. A matching network needs to transform 300 Ω antenna impedance down to 50 Ω.

Where unit confusion actually costs you

Ordering the wrong resistor. A BOM lists a value in kΩ, you search for the ohm value by mistake, and you order a part 1,000 times smaller. On a voltage divider this is a disaster: instead of a 10 kΩ / 22 kΩ divider, you’ve built a 10 Ω / 22 Ω divider that draws 150 mA from your signal source and pulls the voltage rail down. The symptom is usually “the circuit doesn’t work and I don’t know why” until you probe the resistors and find 32 Ω where you expected 32 kΩ.

Misreading a multimeter. Most digital multimeters auto-range and display resistance in Ω, kΩ, or MΩ with a unit indicator on screen. A tired engineer reads the digits without noticing the “k” prefix and records 4.7 Ω instead of 4.7 kΩ. This one’s common enough that it has its own name in certain circles: “prefix blindness.”

Insulation testing at the wrong scale. A megaohmmeter (megger) measures insulation resistance in MΩ. A standard bench multimeter might read up to 40 MΩ or 200 MΩ at its top range. If insulation resistance is 2,000 MΩ (2 GΩ), a bench meter will read “OL” (overload) and you might mistake that for a fault when it’s actually showing the resistance is too high to measure, which is a good thing. Knowing your meter’s range ceiling and converting accordingly matters here.

Confusing resistance with impedance. Resistance is a DC property. Impedance includes both resistance and reactance (from capacitors and inductors), and it changes with frequency. A 10 kΩ resistor has 10 kΩ resistance and approximately 10 kΩ impedance at most frequencies (until parasitic capacitance kicks in). A 10 µF capacitor has an impedance that depends entirely on frequency: at 60 Hz it’s about 265 Ω, at 1 kHz it’s about 15.9 Ω. Converting impedance values in kΩ to Ω uses the same math as resistance conversion, but the values themselves are frequency-dependent. The converter doesn’t know what frequency you’re at; you do.

The standard resistor value series

Resistors aren’t made in every possible value. They’re manufactured in standard series: E12, E24, E48, E96, E192. The number is how many values fit per decade (per ×10 range).

E12 has 12 values per decade: 1.0, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, 8.2. These repeat at every scale: 1 kΩ, 1.2 kΩ, 1.5 kΩ… 10 kΩ, 12 kΩ, 15 kΩ… and so on.

E24 doubles that to 24 values per decade, with tighter spacing. E96 is for 1% tolerance precision resistors. E192 covers 0.1% and tighter.

This matters for unit conversions because it explains why you’ll never find a 5 kΩ resistor in the E12 series, only a 4.7 kΩ and a 5.6 kΩ. If your calculation needs exactly 5 kΩ, you’ll need to either use a non-standard part, combine two standard resistors in series, or adjust your design to work with 4.7 kΩ or 5.6 kΩ.

When you convert your calculated resistance value to the unit on the distributor’s search filter (usually Ω or kΩ), the next step is always rounding to the nearest standard value in your target series. The converter gets you the number; the E-series table tells you which physical part to actually buy.

Conductance: the other side of the same coin

Conductance (G) is 1/R. The unit is the siemens (S), and siemens = 1/ohm. A 1 Ω resistor has 1 S of conductance. A 1,000 Ω (1 kΩ) resistor has 0.001 S = 1 mS of conductance.

Most engineers work almost exclusively in resistance (ohms) and rarely touch siemens. But some contexts prefer conductance.

Transistor datasheets sometimes specify transconductance in siemens (it relates input voltage change to output current change). Network analysis uses admittance matrices, where admittance is conductance plus susceptance (the AC equivalent of conductance). Some older texts on vacuum tube electronics use mhos (mho is just “ohm” spelled backwards, and 1 mho = 1 siemens).

The converter shows conductance in the output panel because when you’re cross-referencing a datasheet that gives transconductance in mS and a simulation tool that works in kΩ, having both values side by side without a separate calculation is actually useful.

The bottom line

Resistance conversions are powers of 1,000. Kilohms to ohms: multiply by 1,000. Ohms to megaohms: divide by 1,000,000. Milliohms to ohms: divide by 1,000. The direction flips depending on whether you’re going up the scale or down.

The two mistakes worth watching: ordering resistors in the wrong unit (your BOM says kΩ, you search in Ω), and misreading a multimeter’s unit prefix when you’re tired. Both produce values that are exactly 1,000 times wrong, which at least makes the error easy to spot once you know to look for it.