Capacitor Calculator

The first two digits are the value in picofarads and the third digit is the number of zeros to append. Code 104 means 10 followed by four zeros: 100 000 pF, which equals 100 nF or 0.1 µF — the most common decoupling capacitor value in electronics. Enter 104 in the converter above to see the tolerance range too.

Divide by 1 000 at each step: 1 000 pF = 1 nF, and 1 000 nF = 1 µF. So a 22 000 pF capacitor is 22 nF or 0.022 µF. The conversion chart above lists the fifteen most common values, and the dedicated capacitance converter tool accepts any value in any unit and displays it in all five at once.

The defining relationship is Q = C × V: the stored charge (Q, in coulombs) equals the capacitance (C, in farads) times the voltage (V, in volts). Rearranged, C = Q / V — one farad is the capacitance that stores one coulomb at one volt. The energy stored is E = ½ × C × V², which the parameters section above computes alongside the charge.

The letter after the numeric code is the EIA tolerance class: J = ±5%, K = ±10%, M = ±20%. Precision codes exist too — B = ±0.1 pF, C = ±0.25 pF, D = ±0.5 pF, F = ±1%, G = ±2% — and Z marks an asymmetric +80%/−20% part typical of large electrolytics. A 104K capacitor is therefore 100 nF with a guaranteed range of 90–110 nF.

Ceramic capacitors are physically tiny, and '0.0000001 F' does not fit on a 2 mm package. The 3-digit code compresses any standard value into three characters: two significant digits plus a power-of-ten multiplier. Values below 10 pF use a decimal R notation instead (4R7 = 4.7 pF), and 1–2 digit codes are read directly in pF.

Out of circuit, a multimeter with a capacitance mode charges the capacitor through a known current and times the voltage ramp. In circuit — for HVAC run capacitors — technicians measure the current through the start winding and the voltage across the capacitor while the motor runs, then compute µF = 2652 × amps ÷ volts at 60 Hz. The capacitor under load calculator on this site runs that formula for you and grades the reading against the rated value, and the guides walk through the method step by step.

For a parallel-plate capacitor, C = K × ε₀ × A / d, where K is the dielectric constant of the material between the plates, ε₀ = 8.854 × 10⁻¹² F/m, A is the overlapping plate area and d the separation. A 1 cm² plate pair 1 mm apart in air is only about 0.088 pF — which is why real capacitors use huge surface areas rolled into tiny cans. The parallel plate calculator on this site runs the formula with 25 dielectric presets, from air and FR-4 to barium titanate.

Capacitors in parallel add directly: C_total = C₁ + C₂ + C₃… — the same rule as resistors in series. Capacitors in series combine by reciprocals: 1/C_total = 1/C₁ + 1/C₂ + 1/C₃…, the mirror of the resistor rule, and the total is always smaller than the smallest capacitor. Series strings also divide voltage across the capacitors, which is how high-voltage banks are built. The series & parallel calculator handles both rules for up to 12 capacitors with mixed units, and the guide library shows the worked examples you can check by hand.

For HVAC run capacitors, stay within about ±5–10% of the rated µF — the motor's start winding current depends on it, and an oversized capacitor overheats the winding while an undersized one loses torque. The voltage rating, however, should be equal or higher than the original; a higher voltage rating is always safe. For decoupling and timing circuits, follow the datasheet — timing values shift proportionally with capacitance.

Several honest reasons: the meter's tolerance is often ±2–5% itself, many capacitors are only guaranteed to ±10% or ±20%, and capacitance drifts with age and temperature. Electrolytics typically lose 10–20% of capacitance over their life. That is exactly why the under-load test method exists — it measures the capacitor while it does real work, at real temperature and real voltage.

In-circuit HVAC testing is live-voltage work: terminals can sit above 300 V even when the unit runs on 240 V mains, and stored charge persists after power-off. Discharge the capacitor through a 20 kΩ 5 W resistor before touching it, never short the terminals directly, and use one hand when probing. If you are not trained for live electrical work, the safer route is a bench test with the capacitor removed.

They are all the same unit spelled differently: µF (microfarad) is often typed uF because µ is hard to produce on a keyboard. Watch out for mF, which formally means millifarad (1 000 µF) but is occasionally misused for microfarad on old or cheap markings — when the context is motor or HVAC capacitors, an 'mF' label almost always means µF. Our converter treats every unit formally: pF, nF, µF, mF and F.

Capacitive reactance is the opposition a capacitor shows to AC, and it falls as frequency rises: X꜀ = 1 / (2πfC). A 100 nF capacitor looks like 31.8 kΩ on a 50 Hz mains line but only 1.59 Ω at 1 MHz. That falling impedance is why capacitors block DC while passing AC signals, and why they make effective noise shunts. Real parts also carry a little series resistance (ESR) and inductance (ESL), so total impedance is |Z| = √(ESR² + X꜀²) until self-resonance, above which the inductance takes over.

Charging is exponential, not linear: V(t) = V₀ × (1 − e^(−t/τ)), where τ = R × C is the time constant in seconds. The capacitor reaches 63.2% of the supply after 1τ, 86.5% after 2τ, and 99.3% after 5τ — engineers call 5τ 'fully charged'. A 100 µF capacitor fed through a 1 kΩ resistor has τ = 0.1 s, so it is effectively full in half a second. Multiply R by C once and you have the whole curve.

Class II ceramics (X7R, X5R, Y5V) lose capacitance under DC bias — the ferroelectric domains in barium-titanate-based dielectric stop polarizing as the electric field strengthens. A 100 µF X7R rated at 50 V can deliver only 30–50 µF near rated voltage. Capacitance meters test at nearly 0 V, so they read the nameplate value. Check the manufacturer's capacitance-vs-voltage curve, use C0G/NP0 for voltage-stable timing, or simply size up the nominal value to keep the effective capacitance you need.

Use E = ½C(V₁² − V₂²), where V₁ is the charged voltage and V₂ the lowest voltage your load tolerates. Example: a 48 V, 100 W controller that must ride through a 16 ms dropout needs E = 1.6 J; from a 54 V charge down to 42 V, C = 2 × 1.6 / (54² − 42²) ≈ 2 800 µF — install 4 000 µF or more for margin. For constant-current loads the simpler t = C(V₁ − V₂)/I applies, and supercapacitors take over where electrolytics run out of farads.

Three ways. Heat shortens life — every 10 °C rise roughly halves an electrolytic's lifetime, which is why a 105 °C-rated part run cool lasts about eight times longer. Cold raises ESR dramatically (5–15× at −40 °C for electrolytics), which can trip a converter on ripple. And Class II ceramics drift strongly across their range while losing extra capacitance under DC bias. Precision timing across temperatures is what C0G/NP0 ceramic and film parts are for.

Equivalent series resistance is the tiny resistance inside the capacitor — leads, plates and dielectric losses lumped into one number. Every amp of ripple current heats the part by P = I²RMS × ESR, so a cap handling 10 A RMS across 50 mΩ dissipates 5 W of heat. High ESR causes voltage ripple, self-heating, and a death spiral in electrolytics where heat evaporates electrolyte, raising ESR further. Power and switching applications always specify low-ESR parts — polymer, ceramic or film.

Read the bands left to right as if on a resistor, but treat the multiplier as picofarads: the first two bands are significant digits, the third multiplies by ten to that power, and an optional fourth band gives tolerance. Brown-red-orange, for example, decodes to 12 × 10³ pF = 12 nF — the same value a printed 123 code would mark. Some vintage mica parts use color dots instead of bands with identical meanings. Decode the bands into the equivalent 3-digit code and enter it in the converter above to see the value in pF, nF and µF with its tolerance range.

Yes — every tool on the site is a free web app that runs entirely in your browser: nothing to install, no account, no paywall. Open it on a phone, tablet or desktop, bookmark it or add it to your home screen, and it behaves like a native capacitor calculator app. The code converter, series and parallel bank tool, parallel-plate calculator and HVAC under-load tester all compute locally on your device, so results update instantly as you type.

It stacks both connection rules: capacitors are wired in series to raise the voltage rating, and identical series strings are then wired in parallel to build the capacitance back up. Example: six 22 µF / 250 V film capacitors arranged as two strings of three — each string measures about 7.3 µF and stands off 750 V, and paralleling the two strings gives roughly 14.7 µF at 750 V. Use matched parts from the same batch, fit a balancing resistor across every string, and model the bank in the series & parallel calculator before building it.