SMD Resistor Code Calculator

The four SMD resistor marking systems

Surface-mount resistors are too small for colour bands, so the value is printed as a short alphanumeric code — or, on 0402 and smaller, not printed at all. Four schemes cover almost everything you will meet on a modern board.

3-digit codes (±5%, E24)

The first two digits are the significant figures and the third is the number of zeros to add. 472 is 47 followed by two zeros — 4,700 Ω, or 4.7 kΩ. 103 is 10 kΩ. 100 is 10 Ω, not 100 Ω, which is the single most common misreading. A code of 000 or 0 marks a zero-ohm link.

4-digit codes (±1%, E96)

Same idea with three significant figures: 4701 is 470 followed by one zero, so 4,700 Ω. 1002 is 100 plus two zeros — 10 kΩ. A four-digit code almost always means a 1% part, which is why the values look like 4.99 kΩ and 2.21 kΩ rather than the round E24 numbers.

R-notation for values below 10 Ω

The letter R stands in for the decimal point, because a printed dot would not survive reflow. 4R7 is 4.7 Ω, 0R22 is 0.22 Ω, R010 is 0.010 Ω. You will see these on current-sense shunts and on the low side of gate drive networks. Some manufacturers use L or M in place of R for milliohm parts — check the datasheet if a shunt reads implausibly high.

EIA-96 codes on 1% precision chips

The smallest 1% parts use a two-digit number plus one letter. The number is a position in the E96 series: 01 means 100, 24 means 174, 96 means 976. The letter is the multiplier — A is ×1, B or H is ×10, C ×100, D ×1 k, E ×10 k, F ×100 k, and S/X ×0.1, R/Y ×0.01, Z ×0.001. So 01C is 100 × 100 = 10 kΩ, and 68X is 499 × 0.1 = 49.9 Ω.

Reading unmarked parts

0402, 0201 and most 0603 resistors on high-density boards carry no marking at all — there is nowhere to print one. The only reliable ways to identify them are the bill of materials, the assembly drawing, or a meter. If you must measure in circuit, lift one end first: parallel paths through the rest of the board will pull your reading low and make a 10 kΩ part look like 4 kΩ.

Package sizes and power ratings

The imperial code on the reel describes the footprint in hundredths of an inch, not the value. Typical ratings at 70 °C:

These are guidance figures — derate above 70 °C and always confirm against the specific manufacturer datasheet, since ratings for the same footprint vary by more than 2:1 between families.

Frequently asked questions

What does 472 mean on an SMD resistor?

It is a 3-digit code: 47 followed by 2 zeros, so 4,700 Ω or 4.7 kΩ. Three-digit codes are almost always ±5% parts from the E24 series.

What is the difference between 100 and 1000 on an SMD resistor?

100 is a 3-digit code meaning 10 Ω (10 followed by zero zeros). 1000 is a 4-digit code meaning 100 Ω (100 followed by zero zeros). Count the digits before you read the value — this pair catches people out constantly.

What does the R mean in 4R7 or 0R22?

R takes the place of the decimal point, because a printed dot would not survive the reflow oven or would be mistaken for dirt. 4R7 is 4.7 Ω and 0R22 is 0.22 Ω. You mostly see this on current-sense shunts.

How do I read an EIA-96 code like 01C?

The two digits are a position in the E96 series (01 = 100, 96 = 976) and the letter is a multiplier (A = ×1, B = ×10, C = ×100, D = ×1 k, and so on). So 01C is 100 × 100 = 10 kΩ. See the E-series reference for the full position table.

Why is my SMD resistor completely unmarked?

0402 and smaller packages have no room to print a code, and many 0603 parts are supplied blank too. Identify them from the bill of materials or the assembly drawing, or measure with one end lifted from the board.

Does a 0-ohm resistor really have zero resistance?

No — it is a jumper with a specified maximum resistance, typically 20 to 50 mΩ, and a current rating of 1 to 2 A depending on package. It exists so a link can be placed by the same pick-and-place machine as everything else.