How to Read a 3-Digit Capacitor Code

Pull a small ceramic capacitor off a circuit board and you will almost never find a value printed on it. What you get instead is a short number like 104, 221, or 473. That number is a code, not a capacitance, and the first time you meet it the math feels like a riddle. It is not. Once you know the rule, you can read any of these markings in a couple of seconds without a chart.

This post walks through exactly how the 3-digit code works, why 104 comes out to 100 nF, how the picofarad / nanofarad / microfarad units stack up, and what those trailing letters mean. By the end you will be able to glance at a code and know what to order or solder back in.

The Rule: Two Significant Figures, Then a Power of Ten

Here is the whole system in one sentence. The first two digits are the significant figures, the third digit is the power of ten, and the result is in picofarads.

That is it. Take the third digit, raise ten to that power, and multiply it by the number formed by the first two digits. The unit is always picofarads (pF) before you do anything else. People trip up most often here, so it is worth saying plainly: the code never resolves directly to nanofarads. It resolves to picofarads, and you convert from there.

A different way to picture the same rule, which a lot of bench technicians find faster: read the first two digits, then add as many zeros as the third digit says. 221 is 22 with one zero added, so 220 pF. 473 is 47 with three zeros, so 47000 pF. Both methods give the same number because multiplying by ten to the power N is the same as appending N zeros.

There is one edge case worth flagging. A tiny value printed as a bare 47 or 33 with no third digit is read literally, so 47 means 47 pF, not 470. Very small ceramics are often marked this way because they have no room for a multiplier digit and no need for one.

Worked Example: Why 104 Is 100nF

104 is the most-searched capacitor code on the planet, and for good reason. It is the default decoupling part scattered across nearly every circuit board ever made. Let us decode it step by step.

• First two digits: 10. That is the significant figure, 10.
• Third digit: 4. That is the exponent, so multiply by ten to the fourth power, which is 10000.
• Result: 10 × 10⁴ = 100000 pF.

So 104 is 100000 picofarads. Now convert up the scale: divide by 1000 to reach nanofarads (100 nF), divide by 1000 again to reach microfarads (0.1 µF). All three describe the exact same part. A datasheet might list it as 100 nF, a supplier as 0.1 µF, and the board silkscreen as nothing at all, just the code. They are identical. If you ever read 104 as "104 nanofarads," you are off by a factor of more than a thousand, which is the classic beginner slip.

If you would rather skip the arithmetic, the Capacitor Code Calculator takes any code and prints the value in pF, nF and µF together, plus the tolerance if a letter is present. It also runs in reverse: type a capacitance and it hands back the code.

How pF, nF and µF Relate

Capacitance units climb in steps of one thousand, which is what makes the conversions clean once you internalize them.

• 1 µF = 1000 nF = 1000000 pF
• 1 nF = 1000 pF
• 100 nF = 0.1 µF = 100000 pF
• 220 pF = 0.22 nF

Each unit has a comfort zone. Picofarads cover the smallest ceramics, the kind you find in oscillators and RF filters. Nanofarads sit in the middle, where the workhorse decoupling and timing parts live, 104 among them. Microfarads belong to the larger electrolytic and tantalum capacitors that smooth power rails. When you stock a parts drawer, decoding each code to its nanofarad value first gives you a single yardstick to sort by, so 103 (10 nF), 104 (100 nF), and 105 (1 µF) line up in order instead of looking like random numbers.

Moving a value between any two units is just shifting a decimal point three places. If you do a lot of these and want a general unit converter for the rest of your bench math, the Unit Converter handles capacitance alongside everything else.

Tolerance Letters: K, J, M and Friends

Sometimes the code carries a trailing letter, like 104K or 221J. That letter is the tolerance, not an extra digit, and you strip it off before decoding the value.

• F = ±1%
• G = ±2%
• J = ±5%
• K = ±10%
• M = ±20%

So 104K is a 100 nF capacitor that may actually measure anywhere from 90 nF to 110 nF, which is fine for decoupling where the exact value barely matters. A 221J is 220 pF held to ±5%, the sort of tighter grade you want in a timing or filter circuit where the value does matter. The mistake to avoid is treating the K in 104K as part of the number; it has nothing to do with the digits and everything to do with the manufacturing spread.

A Word From the Bench

The first time I had to do this for real, I was fixing a cheap guitar pedal that had gone silent. I pulled what turned out to be a 473 from the signal path, stared at it, and confidently decided it was "473 picofarads, near enough." It is not. 473 is 47 followed by three zeros, so 47000 pF, which is 47 nF, a hundred times bigger than my guess. I ordered the wrong part, waited a week, and the pedal stayed dead until the right one arrived. Ever since, I read the third digit as "how many zeros" out loud before I trust myself, and I cross-check anything I am about to order against a calculator. That one wasted week taught the rule better than any chart could.

The same care applies in reverse when you build a parts order from a schematic. A drawing might call for 220 pF, 1 nF and 100 nF, while the bill of materials and the parts themselves use codes. Run each value through the value-to-code direction and you get 221, 102 and 104, which is what to actually write on your storage bins and order envelopes.

Don't Confuse Capacitor Codes With Resistor Codes

One last trap. Capacitor codes and resistor codes look like cousins, and the logic rhymes, but they are not the same. A resistor's third color band is a multiplier on ohms; a capacitor's third digit is a power of ten on picofarads. Mixing them up gives answers that are wrong by orders of magnitude. Keep the two mental models separate: for color-banded resistors reach for the Resistor Color Code Calculator, and for the 3-digit ceramic markings covered here, stick with the capacitor decoder.

With the significant-figures-plus-power-of-ten rule in hand, the picofarad-first habit drilled in, and the tolerance letters separated from the digits, you can now read any 3-digit capacitor code on sight. 104 is 100 nF, 473 is 47 nF, 221 is 220 pF, and you never have to guess on the bench again.

---

Made by Toolora · Updated 2026-06-13