What the SMD Resistor Code Calculator does
Type the code printed on a surface-mount resistor and this tool gives you the resistance, the tolerance class that marking system implies, and the same value written in every other marking system. It handles the three-digit code on 5% parts, the four-digit code on 1% parts, the R notation used for values under 100 ohms, and EIA-96, where two digits and a letter carry a 1% value in three characters.
It works in both directions: enter a value instead and you get the markings to look for on the tape. Everything is a table lookup and a power of ten, done in your browser.
How to use it
- Read the code off the part under good light - the printing is small and 8 and 6 are easy to confuse at 0603 and below.
- Type it into the code box. The resistance, the implied tolerance and the working appear straight away.
- Check the working line. It says which system was recognised and why, which is the fastest way to catch a misread character.
- To go the other way, enter a resistance in the value box and read the marking for each system from the table.
- Compare the value against the E24 and E96 members shown. A marking that decodes to something well away from both is almost always a misread.
Reading the results
The tolerance shown comes from the marking system, not from the part: three digits means the maker was using a 5% scheme and four digits or EIA-96 a 1% scheme. It is a strong convention, not a guarantee, and the reel label is what settles it.
A code of 100 is 10 ohms, not 100 ohms. The last digit is always the number of zeros, so 100 is 10 followed by no zeros. This is the single most common mistake with SMD markings.
An unmarked black chip is usually a zero-ohm link or a very small package with no room for printing. Zero-ohm links are marked 0, 00 or 000 and measure a few tens of milliohms in practice, not literally zero.
Worked example: a chip marked 01C next to one marked 100
01C is EIA-96. The digits 01 are a position in the E96 table, and position 1 is 1.00. The letter C is a multiplier of 100, so the part is 1.00 x 100 = 100 ohms, and because EIA-96 is only used on 1% parts it is a 100 ohm 1% resistor.
The chip next to it marked 100 is the three-digit scheme: 10 followed by zero zeros, which is 10 ohms - a factor of ten smaller, despite looking like the larger number. The two are easy to mix up on a crowded board.
Working backwards, 100 ohms in the other systems is 101 in three digits, 1000 in four digits and 100R in R notation. The calculator lists all of them so you can confirm the part against whatever the reel says.
Formulas and scoring rules
- Three-digit code
R = (first two digits) x 10^(third digit)472 = 47 x 100 = 4.7 kOhm. Normally a 5% part.- Four-digit code
R = (first three digits) x 10^(fourth digit)4701 = 470 x 10 = 4.7 kOhm. Normally a 1% part.- R notation
R marks the decimal point4R7 = 4.7 Ohm, R022 = 0.022 Ohm. K and M are used the same way at higher values: 1K2 = 1.2 kOhm.- EIA-96
R = E96[position] x multiplier(letter)Positions 01-96 index the E96 table; Z x0.001, Y or R x0.01, X or S x0.1, A x1, B or H x10, C x100, D x1k, E x10k, F x100k.
Why EIA-96 exists at all
A 1% resistor needs three significant digits, and three digits plus a multiplier does not fit on an 0402 chip. EIA-96 solves it by numbering the 96 values of the E96 series from 01 to 96 and printing the index instead of the value: 1.00 is 01, 4.99 is 68, 9.76 is 96. A letter then supplies the decade.
The cost is that the code is meaningless without the table - 68C tells you nothing until you know that position 68 is 4.99. That is precisely what this page is for. Note also that two letters share each of three multipliers (Y and R, X and S, B and H); both forms appear in the wild and both are decoded here.
Values below one ohm
Current-sense resistors live in the milliohm range and cannot be expressed as digits plus zeros, so they use R notation with the R in front: R022 is 22 milliohms, R001 is 1 milliohm. Some manufacturers instead use L or M for milliohms on very low values, and a few print the value plainly with a decimal point.
At these values the connection matters as much as the part. A 22 milliohm shunt with 5 milliohms of track and solder in series with it is reading 27 milliohms, which is why sense resistors are four-terminal parts or have Kelvin connections designed into the footprint.
Limitations: what the result does not prove
- The tolerance is inferred from the marking system, not read from the part. Only the reel label, the bag or the manufacturer's part number states it definitively.
- Some manufacturers use their own house codes, particularly on very small packages, on jumpers and on precision parts; those are not decoded here.
- Nothing in the marking gives the power rating, the voltage rating, the temperature coefficient or the package size. Those come from the part number.
- A marking can be ambiguous: 1K2 is unmistakably 1.2 kOhm, but a worn or partly obscured code can read as more than one valid value. Measure when it matters.
Privacy: where your data goes
Everything you paste, type or drop is processed in this browser tab. It is not uploaded, logged, stored or sent to analytics. Session recording and tag-manager scripts are switched off on this page.
Standards and sources
- IEC 60062 - Marking codes for resistors and capacitors - checked 19 Sep 2026
- IEC 60063 - Preferred number series for resistors and capacitors (E series) - checked 19 Sep 2026
- Vishay - Thick film chip resistor data sheet with marking and package ratings
Frequently asked questions
What does 472 mean on an SMD resistor?
47 followed by two zeros: 4,700 ohms, or 4.7 kOhm. The last digit of a three-digit code is always the number of zeros to add, and three-digit markings are normally used on 5% parts.
Why is 100 ten ohms and not one hundred?
Because the third digit is the multiplier, not a digit of the value. 100 is 10 x 10^0 = 10 ohms. One hundred ohms would be marked 101 in the three-digit scheme, or 1000 in the four-digit one.
What does the R mean in 4R7?
R stands in for the decimal point, so 4R7 is 4.7 ohms. The same convention puts the R in front for values below one ohm - R022 is 0.022 ohms - and uses K or M for higher decades, so 1K2 is 1.2 kOhm.
How do I read an EIA-96 code such as 68C?
The two digits are a position in the E96 series and the letter is a multiplier. Position 68 is 4.99 and C is x100, so 68C is 499 ohms. EIA-96 is only used on 1% parts, which is why the tolerance can be stated from the code alone.
What is a resistor marked 000 or 0?
A zero-ohm link: a jumper in a resistor package, used so that a link can be placed by the same pick-and-place machine as everything else. Its actual resistance is a few tens of milliohms and its rating is a current, not a power.
Can I tell a resistor's power rating from the code?
No. The rating comes from the package size - roughly 1/16 W for 0402, 1/10 W for 0603, 1/8 W for 0805 and 1/4 W for 1206 in common ranges - and even then it depends on the maker and the copper the part is soldered to.
The code on my part has four digits but I expected three. Is it still the same value?
Possibly, but read it as a four-digit code: the first three digits are significant and the fourth is the number of zeros. 4701 and 472 are both 4.7 kOhm, but 4700 is 470 ohms, not 4.7 kOhm.
What if the marking has a letter I do not recognise?
Some manufacturers add a suffix for a tolerance class, a date or an internal grade, and a few use house codes on small packages. If the code will not decode here, look it up in the manufacturer's marking guide for that series rather than guessing.
Last reviewed by the A2Z.Tools team against the sources listed above.
