SMD Resistor Code Calculator

Using it in practice

Step by step

1. Read the code on the part with a loupe or a phone camera zoom; note whether it has 3 digits, 4 digits, an R, or two digits and a letter.
2. Type it in and check the decoded value and the format the calculator recognised.
3. To mark or order a part, use the reverse lookup to get the code for a value.

Common mistakes

• Mixing formats. 3-digit "102" is 1 kΩ, but 4-digit "1020" is 102 Ω. The number of digits changes the meaning.
• Missing the R. "4R7" is 4.7 Ω and "R10" is 0.1 Ω; there is no multiplier digit at all.
• Reading an EIA-96 code as 3-digit. Codes such as "01C" (10 kΩ) are two digits plus a letter and mean a 1% part; the digits are an index into the E96 table, not the value.

Practical tips

A part marked "0" or "000" is a zero-ohm jumper. Small 0402 and 0201 parts usually carry no marking at all, so measure them with tweezers probes, ideally before soldering. When a reading in circuit does not match the code, remember that parallel paths on the board lower it; lift one end if you need a true value.

Worked example: reading a small board

• 103 next to a sensor: 10 followed by three zeros, 10 kΩ, most likely a 5% pull-up.
• 4R7 in series with a supply line: 4.7 Ω, often used to limit inrush or as a filter with a capacitor.
• 1001 in a feedback divider: 100 followed by one zero, 1 kΩ, a 1% part because the regulator's output depends on the ratio.
• 68X on a tiny 0603 part: EIA-96 entry 68 is 499, and X means × 0.1, so 49.9 Ω, typical of a termination resistor.
• R010 on a wide 2512 part near a motor driver: 0.010 Ω, a current-sense shunt.

What the marking says about tolerance

The format is a hint about precision. Three-digit codes come from E24 values and usually mean 5% (sometimes 1% parts carry them too). Four-digit codes and EIA-96 codes are used on 1% parts, because the E96 series needs three significant digits. Where accuracy matters, such as a regulator feedback divider or an ADC input, replace a part with one of the same or tighter tolerance rather than the same value in a looser one. When you order replacements, the size code (0402, 0603, 0805) tells you the footprint, and the power rating follows it, from about a sixteenth of a watt for 0402 to an eighth for 0805.