Capacitor Code Calculator

Capacitor code calculator: from 104 to 100 nF and back

Small capacitors carry a short capacitor code: three digits such as 104, a tolerance letter such as K, sometimes a voltage code such as 1H and a temperature code such as X7R. This capacitor code calculator decodes all four and shows the value in pF, nF and µF with the tolerance range, rating and temperature behaviour.

It also runs in reverse (100 nF → 104K), totals capacitors in series or parallel, and covers the everyday maths — charge Q = CV, energy ½CV² and an RC time constant calculator that also handles RL circuits, with the charge/discharge curve and the cut-off frequency.

Codes follow the EIA-198 and IEC 60062 conventions; everything is computed in your browser.

How to use the Capacitor Code Calculator

1. Type the printed code into “Capacitance code” — digits with or without a tolerance letter (104, 104K, 472J, 22, 4R7, 2n2).
2. Optionally add the voltage code (1H, 2A, 50V) and temperature code (X7R, C0G).
3. Read the result; the charts below it list every letter code.
4. Switch to “Value → code” to label a part, “Series / parallel” to combine capacitors, “Charge, energy & RC” for Q and E, or “RC / RL time constant” for τ, the curve, the time to a chosen percentage and the C or L for a target cut-off.

Capacitor Code Calculator features

How the 3-digit capacitor code works

The first two digits are the significant figures and the third is the number of zeros, giving a value in picofarads: 104 = 10 followed by 4 zeros = 100 000 pF = 100 nF = 0.1 µF. Third digits 8 and 9 mean ×0.01 and ×0.1, so 229 is 2.2 pF. Values below 10 pF use R for the decimal point (4R7 = 4.7 pF), and European markings use the unit letter in the same way (2n2 = 2.2 nF, 4u7 = 4.7 µF).

Tolerance, voltage and temperature letters

• Tolerance: B ±0.1 pF, C ±0.25 pF, D ±0.5 pF, F ±1 %, G ±2 %, H ±3 %, J ±5 %, K ±10 %, M ±20 %, Z +80/−20 %. So 104K is 100 nF ±10 % — anywhere from 90 to 110 nF.
• Voltage (digit + letter): 0J 6.3 V, 1A 10 V, 1C 16 V, 1E 25 V, 1V 35 V, 1H 50 V, 1J 63 V, 2A 100 V, 2E 250 V, 2G 400 V, 2J 630 V. Rate parts well above the circuit voltage.
• Class 2 temperature codes (EIA-198): first letter = low temperature (X −55 °C, Y −30 °C, Z +10 °C), digit = high temperature (5 +85 °C, 6 +105 °C, 7 +125 °C), last letter = maximum capacitance change (R ±15 %, S ±22 %, U +22/−56 %, V +22/−82 %). Y5V and Z5U drift a lot.
• Class 1 codes: C0G (NP0) means 0 ±30 ppm/°C — very stable, used for timing and filters.

Capacitor formulas used here

Parallel capacitors add: C = C₁ + C₂ + …. In series the reciprocals add: 1/C = 1/C₁ + 1/C₂ + …, so two 10 µF parts in series give 5 µF. Charge Q = C·V and energy E = ½·C·V²: a 100 µF capacitor at 12 V stores 1.2 mC and 7.2 mJ. The 555 timer calculator builds on the RC relationship, and the resistor colour code calculator decodes the resistor side.

RC time constant formula, RL circuits and frequency

The time constant is τ = R·C for a resistor and capacitor, or τ = L/R for a resistor and inductor. After one τ a charging capacitor reaches 63.2 % of the supply (v = V·(1 − e^(−t/τ))); after 5τ it is above 99 % and usually treated as full. Discharging follows e^(−t/τ), and the time to any level is t = −τ·ln(1 − p) charging or −τ·ln(p) discharging. To go from RC time constant to frequency, f_c = 1/(2πτ): 1 kΩ with 100 nF, or 100 Ω with 10 mH, gives τ = 100 µs and f_c ≈ 1.59 kHz. These are ideal first-order formulas; real parts add tolerance, ESR and leakage.