Resistor SMD Code Calculator: How to Read

This calculator decodes the three- or four-digit code printed on surface-mount (SMD) resistors and returns the resistance value in ohms, along with the tolerance if a letter is present. You enter the code exactly as printed (for example, 472 or 1002), and the calculator gives you the resistance in ohms, kilohms, or megahms, plus the tolerance for EIA-96 and similar letter-coded parts. The tool also handles the EIA-96 code, which uses a two-digit number and a letter to represent a value from a standard table.

Formula

For a standard three- or four-digit SMD code, the first two or three digits are the significant figures, and the last digit is the multiplier (power of ten). The resistance in ohms is:

R = (first digits) × 10^{last digit}

• R – resistance in ohms (Ω)
• first digits – the leading digits of the code (e.g., “47� in “472�)
• last digit – the exponent of the multiplier (e.g., “2� in “472� means ×10²)

For the EIA-96 code, the first two digits are an index into a standard table of values (from 100 to 976), and the letter indicates the multiplier (e.g., A=10�, B=10¹, C=10², D=10³, E=10�, F=10�, X=10�¹, Y=10�², Z=10�³). The calculator uses that table internally.

Worked Example

Take the default code 472:

1. Significant digits: 47
2. Multiplier: 10² = 100
3. Resistance = 47 × 100 = 4700 Ω (or 4.7 kΩ)

The calculator returns 4700 ohms, which matches the standard value for a 4.7 kΩ resistor. For a code like 1002, the first three digits are 100 and the multiplier is 10², giving 100 × 100 = 10,000 Ω (10 kΩ).

How SMD Resistor Codes Work

Surface-mount resistors are tiny – often just a few millimeters long – so printing the full resistance value like “4.7kΩ� is impractical. Instead, manufacturers use a compact numeric code. The most common system is the three-digit code for values with 5% tolerance and the four-digit code for 1% tolerance parts. The first two (or three) digits are the significant figures, and the last digit is the multiplier. For example:

• 221 = 22 × 10¹ = 220 Ω
• 332 = 33 × 10² = 3300 Ω (3.3 kΩ)
• 473 = 47 × 10³ = 47,000 Ω (47 kΩ)
• 1004 = 100 × 10� = 1,000,000 Ω (1 MΩ)

For values below 10 Ω, the letter R is used to indicate the decimal point. For instance, 4R7 means 4.7 Ω, and R22 means 0.22 Ω. The calculator treats R as a decimal point in that context.

EIA-96 Code for 1% Resistors

When a 1% tolerance resistor is too small for a four-digit code, manufacturers use the EIA-96 system. This uses two digits (from 01 to 96) and a letter (from A to H, R, S, X, Y, Z). The two digits refer to a row in a standard table of values – for example, 01 = 100, 02 = 102, 03 = 105, and so on up to 96 = 976. The letter gives the multiplier:

• Z = ×0.001 (10�³)
• Y = ×0.01 (10�²)
• X = ×0.1 (10�¹)
• A = ×1 (10�)
• B = ×10 (10¹)
• C = ×100 (10²)
• D = ×1000 (10³)
• E = ×10000 (10�)
• F = ×100000 (10�)

For example, code 49C means the value at index 49 is 316, and the multiplier C is ×100, so the resistance is 316 × 100 = 31,600 Ω (31.6 kΩ). The calculator includes this table and can decode any EIA-96 code you enter.

How to Use the Calculator

Enter the code exactly as printed on the resistor. The calculator accepts:

• Three-digit codes (e.g., 472, 221)
• Four-digit codes (e.g., 1002, 4701)
• Codes with the letter R (e.g., 4R7, R22)
• EIA-96 codes (e.g., 49C, 01A)

If you enter a code that doesn’t match any known pattern, the calculator will show an error message. For EIA-96 codes, the tolerance is always 1% (the letter does not indicate tolerance – it’s the multiplier). For three- and four-digit codes, the tolerance is typically 5% and 1% respectively, but the calculator does not assume a tolerance unless you see a letter like J (5%) or F (1%) printed separately.

Common Mistakes and Tips

• Misreading the multiplier: The last digit is a power of ten, not a number to multiply directly. For example, 472 is 47 × 10² = 4700 Ω, not 47 × 2 = 94 Ω.
• Confusing R with a letter code: In three-digit codes, R is a decimal point, not a multiplier. 4R7 is 4.7 Ω, not 47 Ω.
• Assuming tolerance from the code: The numeric code does not encode tolerance. A separate letter (J, K, F, D) is often printed after the value, but many small resistors omit it.
• Using the wrong table for EIA-96: The EIA-96 table is specific – you cannot decode it by treating the two digits as a simple number. Always use the standard table.
• Ignoring the unit: The calculator returns ohms. If you need kilohms or megohms, divide by 1000 or 1,000,000 respectively.

Limitations of SMD Codes

Not every SMD resistor uses the numeric code. Some very small sizes (like 0201) may not have any marking at all, and you must measure them with a multimeter. Also, some manufacturers use a different coding system, such as the EIA-96 for 1% parts, but there is also a less common two-digit plus letter system for 2% and 5% parts that is not covered here. The calculator handles the two most common systems: three/four-digit and EIA-96.

Frequently Asked Questions

What does the letter R mean in an SMD code?

R is used as a decimal point, not a multiplier. For example, 4R7 means 4.7 Ω, and R22 means 0.22 Ω. This is common for values below 10 Ω where a decimal point would be hard to print.

How do I read a code like 1002?

1002 is a four-digit code: the first three digits (100) are the significant figures, and the last digit (2) is the multiplier. So 100 × 10² = 10,000 Ω, or 10 kΩ.

What is the tolerance of an SMD resistor with code 472?

The numeric code alone does not indicate tolerance. Typically, three-digit codes are 5% (J) and four-digit codes are 1% (F), but you should check the separate tolerance letter if present. The calculator does not assume a tolerance for three/four-digit codes.

Can I use this calculator for EIA-96 codes?

Yes, the calculator includes the EIA-96 table. Enter the two-digit number and the letter (e.g., 49C) and it will return the resistance value. The tolerance for EIA-96 parts is always 1%.

Why does my resistor have no marking?

Very small SMD resistors (like 0201 size) often have no marking because there isn’t enough space. In that case, you must measure the resistance with a multimeter or refer to the circuit board schematic.

What if I enter an invalid code?

The calculator will show an error. Common reasons are a code that is not three/four digits, or an EIA-96 code with a number outside 01–96 or a letter outside the allowed set (A–H, R, S, X, Y, Z).

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in code | Resistor code | - | 472 | 0
out value | Resistance | ohm | 47 * 10^2 | 0
out tolerance | Tolerance | % | 0 | 0