SMD resistor code calculator
By Robolab Technologies In More Info, Self Learning MaterialLink: http://www.hobby-hour.com/electronics/smdcalculator/smd-resistor-calc.php
This simple calculator will help you determine the value of any SMD resistor. To get started, input the 3 or 4 digit code and hit the “Calculate” button or Enter.
Note: The program was tested rigorously, but it still may have a few bugs. So, when in doubt (and when it’s possible) don’t hesitate to use a multimeter to double-check the critical components. See also the color code calculator on this page for MELF and standard through-hole resistors.
How to calculate the value of an SMD resistor
Most chip resistors are marked with a 3-digit or 4-digit code — the numerical equivalent of the familiar color code for through-hole components. Recently, a new coding system (the EIA-96) has appeared on precision SMDs.
The 3-digit code
Standard-tolerance SMD resistors are marked with a simple 3-digit code. The first two numbers will indicate the significant digits, and the third will be the multiplier, telling you the power of ten to which the two significant digits must be multiplied (or how many zeros to add). Resistances of less than 10 ohms do not have a multiplier, the letter ‘R’ is used instead to indicate the position of the decimal point.
3-digit code examples:
220 = 22 × 100 (1) = 22Ω (not 220Ω!)
471 = 47 × 101 (10) = 470Ω
102 = 10 × 102 (100) = 1000Ω or 1kΩ
3R3 = 3.3Ω
more 3-digit SMD resistor examples…
The 4-digit code
The 4-digit code is used for marking precision surface mount resistors. It’s similar to the previous system, the only difference is the number of significant digits: the first three numbers will tell us the significant digits, and the fourth will be the multiplier, indicating the power of ten to which the three significant digits must be multiplied (or how many zeros to add). Resistances of less than 100 ohms are marked with the help of the letter ‘R’, indicating the position of the decimal point.
4-digit code examples:
4700 = 470 × 100 (1) = 470Ω (not 4700Ω!)
2001 = 200 × 101 (10) = 2000Ω or 2kΩ
1002 = 100 × 102 (100) = 10000Ω or 10kΩ
15R0 = 15.0Ω
more 4-digit SMD resistor examples…
EIA-96
Recently, a new coding system (EIA-96) has appeared on 1% SMD resistors. It consists of a three character code: the first 2 numbers will tell us the 3 significant digits of the resistor value (see the lookup table below) and the third marking (a letter) will indicate the multiplier.
| Code | Multiplier |
|---|---|
| Z | 0.001 |
| Y or R | 0.01 |
| X or S | 0.1 |
| A | 1 |
| B or H | 10 |
| C | 100 |
| D | 1000 |
| E | 10000 |
| F | 100000 |
EIA-96 code examples:
01Y = 100 × 0.01 = 1Ω
68X = 499 × 0.1 = 49.9Ω
76X = 604 × 0.1 = 60.4Ω
01A = 100 × 1 = 100Ω
29B = 196 × 10 = 1.96kΩ
01C = 100 × 100 = 10kΩ
more EIA-96 SMD examples…
Notes:
- an SMD resistor with a marking of 0, 00, 000 or 0000 is a jumper (a zero-ohm link).
- a chip resistor marked with the standard 3 digit code and a short bar below the marking denotes a precision (1% or less) resistor with a value taken from the E24 series (these values are usually reserved for 5% resistors). For example: 122 = 1.2kΩ 1%. Some manufacturers underline all three digits — do not confuse this with the code used on low value current sensing resistors.
- SMDs with values in order of milliohms, made for current sensing applications are often marked with the help of the letter M or m, showing the decimal point location (with the value in milliohms). For example: 1M50 = 1.50mΩ, 2M2 = 2.2mΩ.
- Current sensing SMDs can also be marked with a long bar on top (1m5 = 1.5mΩ, R001 = 1mΩ, etc.) or a long bar under the code (101 = 0.101Ω, 047 = 0.047Ω). The underline is used when the starting ‘R’ has to be omitted due to the limited space on the resistor’s body. So, for example, R068 becomes 068 = 0.068Ω (68mΩ).
Power rating
To find out the approximative power rating of your SMD resistor, measure its length and width. A few commonly used package dimensions with the corresponding typical power ratings are presented in the table below. Use this table as a guide only, and always consult the component’s datasheet for the exact value.
| Package | Size in inches (L×W) | Size in mm (L×W) | Power rating |
|---|---|---|---|
| 0201 | 0.024″ × 0.012″ | 0.6 mm × 0.3 mm | 1/20W |
| 0402 | 0.04″ × 0.02″ | 1.0 mm × 0.5 mm | 1/16W |
| 0603 | 0.063″ × 0.031″ | 1.6 mm × 0.8 mm | 1/16W |
| 0805 | 0.08″ × 0.05″ | 2.0 mm × 1.25 mm | 1/10W |
| 1206 | 0.126″ × 0.063″ | 3.2 mm × 1.6 mm | 1/8W |
| 1210 | 0.126″ × 0.10″ | 3.2 mm × 2.5 mm | 1/4W |
| 1812 | 0.18″ × 0.12″ | 4.5 mm x 3.2 mm | 1/3W |
| 2010 | 0.20″ × 0.10″ | 5.0 mm × 2.5 mm | 1/2W |
| 2512 | 0.25″ × 0.12″ | 6.35 mm × 3.2 mm | 1W |
Tolerance
The standard 3 and 4 digit code does not give us a way to determine the SMD resistor’s tolerance. In most cases, however, you’ll find that a surface mount resistor marked with the 3-digit code has a tolerance of 5% and a resistor marked with 4-digit code or the new EIA-96 code has a tolerance of 1% or less. There are many exceptions to this rule, so always check the manufacturer’s datasheet, especially if the component’s tolerance is critical for your application.
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