Capacitor calculator
Decode a printed code like 104, then get reactance at frequency, RC time constant, charge and stored energy.
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That code means
100 nF
The value is in picofarads before conversion.
Reactance at that frequency
1.59 kΩ
Xc = 1 ÷ (2πfC). How much the capacitor opposes AC — it falls as frequency rises.
Time constant (RC)
1 ms
63% of the way there. Five of these is fully charged.
Charge stored
500 nC
Q = C × V
Energy stored
1.25 µJ
E = ½CV²
The voltage printed on a capacitor is a maximum, not an operating point. Run an electrolytic at no more than about two thirds of its rating — a 12 V rail wants a 25 V part. And check the dielectric code: an X7R or Y5V ceramic loses a large part of its value with temperature and applied voltage, so a timing circuit built with one will not match this arithmetic.
Where this comes from
The number is the easy part. If you have to explain it to a panel, read the write-up — it goes through the formula, the assumptions and the mistakes that make the answer wrong.
Capacitor codes and markingsWhat 104, 22p and 10uF 25V actually mean, the tolerance and dielectric letters, and which way round a polarised capacitor goes.Other calculators
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