Check a 1 ohm resistor in the calculator
The calculator is set to 1 Ω with a gold tolerance band. Switch to 5 or 6 bands, change the tolerance, or choose “Read the bands” to decode a resistor you are holding.
1 ohm resistor colour bands
A 1 Ω resistor carries the same value in every marking system; only the number of bands changes. Read from the end with the bands bunched closest to it, with the tolerance band, usually gold or brown and set slightly apart, on the right.
| Marking | Colours | Drawing | Where you see it |
|---|---|---|---|
| 4 bands, ±5 % | brown, black, gold, gold | The most common through-hole marking | |
| 5 bands, ±1 % | brown, black, black, silver, brown | Precision metal-film resistors | |
| 6 bands, ±1 %, 100 ppm/K | brown, black, black, silver, brown, brown | Adds a temperature-coefficient band | |
| 3 bands, ±20 % | brown, black, gold | Old parts with no tolerance band |
How to read brown, black, gold, gold
- First band, brown: first digit 1.
- Second band, black: second digit 0, giving 10.
- Third band, gold: multiply by 0.1, giving 1 Ω.
- Fourth band, gold: tolerance ±5 %.
On the 5-band version the first three bands are digits (100) and the fourth is the multiplier (×0.01), which comes to the same 1 Ω. Check any other combination with the resistor color code calculator.
What a 1 ohm resistor should measure
Tolerance is how far the real resistance may sit from the marked value. Measured out of circuit with a meter, a good 1 Ω resistor reads within these limits:
| Tolerance | Band | Lowest | Highest |
|---|---|---|---|
| ±1 % | Brown | 990 mΩ | 1.01 Ω |
| ±2 % | Red | 980 mΩ | 1.02 Ω |
| ±5 % | Gold | 950 mΩ | 1.05 Ω |
| ±10 % | Silver | 900 mΩ | 1.1 Ω |
| ±20 % | None (no band) | 800 mΩ | 1.2 Ω |
At 1 Ω the meter leads matter: two leads and their contacts typically add a few tenths of an ohm, which is a large share of the reading. Short the probes together first and subtract that figure, or use the meter’s relative (REL) mode.
Is 1 ohm a standard resistor value?
Yes. 1 Ω belongs to the E3, E6, E12, E24, E48, E96, E192 series of IEC 60063, so it is made in every tolerance from ±20 % down to ±0.1 %. The neighbouring E12 values are 820 mΩ below and 1.2 Ω above. All the series are listed on our E-series resistor values page.
SMD code for 1 Ω
- 3-digit code (usually ±5 %):
1R0. - 4-digit code (usually ±1 %):
1R00. - EIA-96 code (±1 % chips in 0603 and smaller):
01Y: code 1 for the digits, the letter for the multiplier.
Decode any chip marking with the SMD resistor code calculator.
Current, power and wattage
A 1 Ω resistor is sized by the current through it: V = I × R and P = I² × R.
| Current | Voltage | Power | Rating to use |
|---|---|---|---|
| 0.1 A | 100 mV | 10 mW | ⅛ W |
| 0.5 A | 500 mV | 250 mW | ½ W |
| 1 A | 1 V | 1 W | 2 W |
| 2 A | 2 V | 4 W | a power resistor |
A ¼ W 1 Ω resistor reaches its full rating at 0.5 V (V = √(P × R)), or 500 mA (I = √(P ÷ R)).
What a 1 ohm resistor is used for
A 1 Ω resistor is the classic current-sense resistor: in series with a supply, the voltage across it in volts equals the current in amps, so a voltmeter or oscilloscope reads current directly. It also limits inrush in small power supplies and damps resonances in filters. Choose its wattage from I²R: 1 A through it dissipates 1 W.
Mistakes when reading a 1 ohm resistor
The multiplier band moves the value by a factor of ten for every colour step, so it is the band to check twice, in good light. These are the misreadings that catch people out with 1 Ω:
- Gold read as silver. Brown, black, silver, gold would be 100 mΩ, 10 times too low.
- Reading the 4-band code backwards. It can’t be done: gold is not a digit colour, which is how you know which end comes first.
- Reading the 5-band code backwards. The reversed sequence is not a valid code, so the orientation is unambiguous.
Making 1 Ω from other values
No 1 Ω in the drawer? Two common E12 values can stand in, within 1 %: in series, 180 mΩ + 820 mΩ = 1 Ω; in parallel, 1.8 Ω ∥ 2.2 Ω = 990 mΩ. Two 1 Ω resistors give 2 Ω in series and 500 mΩ in parallel.
Colour codes for other common values
- 100 ohm resistor: brown, black, brown
- 220 ohm resistor: red, red, brown
- 330 ohm resistor: orange, orange, brown
- 470 ohm resistor: yellow, violet, brown
- 1k resistor: brown, black, red
- 4.7k resistor: yellow, violet, red
- 10k resistor: brown, black, orange
- 100k resistor: brown, black, yellow
- 1M resistor: brown, black, green
Colours follow IEC 60062:2016. Codes, ranges and currents on this page are computed by the same engine as the resistor colour code calculator; see our methodology.