SMD Resistor Code Calculator

Method, formulas and references

3-digit and 4-digit codes

The last digit is the power of ten and the digits before it are the significant figures. 472 is 47 × 10² = 4.7 kΩ and 4701 is 470 × 10¹ = 4.7 kΩ. A 3-digit code usually marks a ±5 % part and a 4-digit code a ±1 % part, but the tolerance is not part of the code. 000 or 0 is a zero-ohm jumper.

R and m notation

Below 10 Ω (3-digit) or 100 Ω (4-digit) the letter R marks the decimal point: 4R7 = 4.7 Ω, R10 = 0.1 Ω, 47R5 = 47.5 Ω. Current-sense resistors often use a lower-case m for milliohms: 5m0 = 5.0 mΩ.

EIA-96

Small 1 % resistors (0603 and below) cannot fit four digits, so they use EIA-96: two digits give the position of the value in the E96 series (01 = 100, 02 = 102 … 96 = 976) and a letter gives the multiplier. 01C = 100 × 100 = 10 kΩ; 68X = 499 × 0.1 = 49.9 Ω.

R and S are alternatives for Y and X, and H for B. That makes a code such as 10R ambiguous: EIA-96 reads it as 124 × 0.01 = 1.24 Ω, while R notation reads 10 Ω. The calculator shows both; the part's size and the other resistors on the board usually decide.

References

1. IEC 60062:2016, Marking codes for resistors and capacitors.
2. EIA-96 marking code for 1 % surface-mount resistors, with the E96 series of IEC 60063.