SMD Resistor Codes Explained: 3-Digit, 4-Digit and EIA-96

Reading chip resistor markings: the power-of-ten 3-digit code, the 1% 4-digit code, R as a decimal point, and the EIA-96 index-plus-letter system used on 0603 parts.

2026-10-29 · 9 min read

A through-hole resistor tells you its value with colour bands. A surface-mount chip resistor has no room for bands, so it carries a tiny printed code, or on the smallest sizes nothing at all. Three marking systems cover nearly every part you will meet, and once you know which one you are looking at, each takes seconds to read. This guide explains all three, the letter R as a decimal point, and the traps that catch people during repair work. The SMD Resistor Code Calculator decodes and encodes every format described here.

The three systems at a glance

The right-hand column is the key to why three systems exist. Resistor values are not arbitrary: they follow the preferred number series of IEC 60063. The E24 series has 24 values per decade with two significant figures (1.0, 1.1, 1.2, 1.3, 1.5 ...), which suits ±5% parts. The E96 series has 96 values with three significant figures (1.00, 1.02, 1.05, 1.07 ...), which suits ±1% parts. A marking system has to carry enough digits for the series it serves.

The 3-digit code

The first two digits are the significant figures and the third is the number of zeros to add, the same rule as the colour code and ceramic capacitor codes.

• 100 = 10 × 10⁰ = 10 Ω
• 221 = 22 × 10¹ = 220 Ω
• 103 = 10 × 10³ = 10 kΩ
• 474 = 47 × 10⁴ = 470 kΩ
• 105 = 10 × 10⁵ = 1 MΩ

A common slip is reading 100 as 100 Ω. It is ten ohms: one, zero, and no zeros added. 101 is 100 Ω.

Values under 10 Ω cannot be written this way because the multiplier cannot go negative on resistors. Instead the letter R replaces the decimal point: 4R7 is 4.7 Ω, 1R0 is 1.0 Ω and R47 is 0.47 Ω. Third digits of 8 and 9, which mean ×0.01 and ×0.1 on some capacitors, are not used on resistors, so a code like 109 is usually 601 read upside down.

The 4-digit code

Four digits work the same way with three significant figures: the first three digits and then the number of zeros.

• 1000 = 100 × 10⁰ = 100 Ω
• 4991 = 499 × 10¹ = 4.99 kΩ
• 1002 = 100 × 10² = 10 kΩ
• 1213 = 121 × 10³ = 121 kΩ

Below 100 Ω the R takes over again: 47R5 is 47.5 Ω, 4R70 is 4.70 Ω and R100 is 0.100 Ω. Current-sense resistors use the four-character R codes heavily: R010 is 10 mΩ, R005 is 5 mΩ.

The EIA-96 code

On an 0603 (1.6 × 0.8 mm) part, four characters are too many to print legibly. The EIA-96 system squeezes a 1% value into three: two digits that are the value's position in the E96 table, followed by a letter multiplier.

The index is the hard part to remember, so here is a slice of the E96 table:

Worked readings: 01C = 100 × 100 = 10.0 kΩ. 68X = 499 × 0.1 = 49.9 Ω. 30H = 200 × 10 = 2.00 kΩ (H is the alternative letter for B). 09C = 121 × 100 = 12.1 kΩ. The calculator holds the full 96-entry table, with a filter to look up any code.

Because the two digits count from 01 to 96, codes like 00C or 97A cannot exist. If you read one, look again under magnification.

Going the other way: which code will a value have?

Encoding is decoding run backwards, with one catch: not every value has an exact code in every family.

• 10 kΩ: 3-digit 103, 4-digit 1002, EIA-96 01C. All exact.
• 4.7 Ω: 3-digit 4R7, 4-digit 4R70. 4.7 is not an E96 value, so the nearest EIA-96 code is 66Y (4.75 Ω, +1.1%).
• 12.1 kΩ: 4-digit 1212 and EIA-96 09C are exact, but the 3-digit code can only say 123 (12 kΩ, 0.83% low), because two figures cannot hold 12.1.

So if a BOM calls for 12.1 kΩ and the reel says 123, someone substituted an E24 part. Whether that matters depends on the circuit: in a feedback divider setting a regulator's output, it shifts the voltage by nearly 1%.

Ambiguous codes and other traps

Upside-down codes. 0603 text is barely 0.5 mm tall. 601 upside down reads 109, and 106 reads 901. When a reading gives an unlikely value or an impossible digit, rotate the board.

Trailing R. A code like 47R fits the EIA-96 pattern (47 = 301, R = ×0.01, so 3.01 Ω), but a few older parts used a trailing R simply to mean "ohms", so 47R meant 47 Ω. Measure if the circuit makes either plausible. The calculator reads it as EIA-96 and shows the warning.

Zero-ohm links. 0, 00, 000 or 0000 marks a jumper. Its resistance is tens of milliohms and it is specified by current, often 1 A or more for an 0603 part.

Unmarked parts. Most 0402 and 0201 resistors have no marking at all. The reel label is the only record, so keep cut tape labelled.

Maker-specific codes. Some precision, automotive and thin-film ranges use the maker's own marking. If a code fits none of the systems here, look up the marking table in the maker's datasheet.

Measuring to confirm

A code tells you what the part should be, not whether it still is. Resistors fail open or drift after overheating. Measure out of circuit, or lift one end with a soldering iron; in circuit, any parallel path makes the meter read low. For values under 1 Ω use a four-wire (Kelvin) measurement or a meter with a low-ohms range, because test lead resistance is comparable to the part.

A short history

The 3-digit scheme borrows from the colour code that dates to the 1920s Radio Manufacturers Association, the predecessor of the EIA. The E-series preferred numbers were standardised internationally as IEC 63 in 1952, now IEC 60063. EIA-96 marking spread as chip sizes shrank and remains the usual way to mark 1% parts too small for four characters.

Sources

• IEC 60063, Preferred number series for resistors and capacitors (E6 to E192).
• Resistor makers' chip resistor marking guides describing 3-digit, 4-digit and EIA-96 codes.

For through-hole parts with bands, use the Resistor Color Code Calculator; for ceramic and film capacitor markings, the Capacitor Code Calculator. Our series and parallel guide covers combining values once you know them.

Open the SMD Resistor Code Calculator