One Capacitance Value, Five Units, One Code
The same capacitor is 100 000 pF on the reel, 100 nF on a European datasheet, 0.1 µF on an American schematic and code 104 on the part itself. Type any one of those forms below and the converter shows all the others at once — plus the tolerance letter range the marking promises.
Capacitance Unit & Code Converter
Type once — pF, nF, µF, mF, F and the closest EIA code all update live.
Closest 3-digit code: 101 (≈ 100 pF) — 104 pF rounds to two significant digits plus a power of ten.
Range: 90000 – 110000 pF
A 104K is therefore guaranteed between 90 and 110 nF. The letter is a promise about the manufacturing band, not the value.
Why Capacitors Need Five Units at All
The farad is defined by physics, not by convenience: one farad stores one coulomb of charge at one volt. That definition made sense on paper in the 1860s and was instantly impractical in the workshop — a whole farad in a conventional component would fill a filing cabinet. Every useful capacitor therefore lives far down the metric ladder, and engineers reached for the prefixes that kept the numbers readable.
The historical mess is that the ladder was populated in stages. Microfarads came first, written µF or — when the label printer had no Greek — uF, MFD or mFD. Picofarads were called micromicrofarads (µµF) until 1960, when the SI system formally introduced pico. Nanofarads arrived with IEC standardisation and were adopted enthusiastically in Europe and never really caught on in American drafting rooms. The result is five live units and four regional habits, all describing the same physics.
Each step on the ladder differs by exactly one thousand, which is the saving grace: every conversion is three decimal places per hop, and mistakes come from picking the wrong starting rung, not from hard arithmetic. The converter removes even that risk by showing every rung simultaneously.
Every marking is a value in disguisePhoto: UnsplashThe Five Rungs, in Their Natural Habitat
Each unit owns a range of the component world. Knowing which rung a family of parts lives on is half of reading any marking correctly.
1 pF = 1e-12 F
The native unit of ceramic and mica caps. Markings, datasheets and the 3-digit code all count in picofarads first — everything else is a conversion away.
1 nF = 1e-9 F
The European workhorse. A 104 code is 100 nF, and most film caps between 1 nF and 1 µF are quoted in nanofarads on EU datasheets.
1 µF = 1e-6 F
The unit of electrolytics, film caps and motor run capacitors. If a schematic says '10µ' with no prefix drama, this is the unit it means.
1 mF = 1e-3 F
Rarely used honestly. On modern parts it means millifarads; on old motor labels it usually meant microfarads. Check the section below before trusting it.
1 F = 1e+0 F
One farad is enormous — a supercapacitor territory. Whole farads back up real-time clocks and ride through power dips, not filter audio.
The 3-Digit Code: a Value in Three Characters
A capacitor body is small, the printing process is crude, and the value must survive handling. The EIA Class 2 marking system compresses everything into three digits: the first two are the significant figures in picofarads, and the third is the number of zeros that follow. Code 104 is therefore 10 followed by four zeros — 100 000 pF, better known as 100 nF or 0.1 µF. The scheme is identical to the resistor colour code in spirit, except the digits are printed plainly instead of encoded as colours.
Two edge cases complete the system. Codes of one or two digits read directly in picofarads — a cap marked 22 is 22 pF, because appending a zero would lie about its value. And below 10 pF, where decimals are unavoidable, the decimal point is written as the letter R: 4R7 is 4.7 pF and R50 is 0.5 pF. The converter above handles both directions, including the R-notation cases that trip up hand-made lookup tables.
| Marking | In pF | Readable as | Where you meet it |
|---|---|---|---|
| 104 | 100 000 pF | 100 nF = 0.1 µF | The decoupling cap on practically every board ever made. |
| 473 | 47 000 pF | 47 nF | Timing and coupling — the classic 473K marked cap. |
| 221 | 220 pF | 0.22 nF | RF circuits and crystal oscillators. |
| 105 | 1 000 000 pF | 1 µF | Bulk decoupling and low-frequency filtering. |
| 224 | 220 000 pF | 220 nF | European schematics' favourite coupling value. |
| 4R7 | 4.7 pF | R-notation below 10 pF | The decimal point becomes an R because there is no room for one. |
104 → 10 × 10⁴ pF = 100 000 pF = 100 nF = 0.1 µF
473 → 47 × 10³ pF = 47 000 pF = 47 nF
4R7 → 4.7 pF (R-notation below 10 pF)
The Letter After the Code: a Promise, Not a Value
The digit code gives the nominal value; the letter that follows gives the manufacturing band the actual part is guaranteed to fall inside. A 104K is not a 100 nF capacitor — it is a capacitor somewhere between 90 and 110 nF. The EIA letter system runs from fractions of a picofarad on precision parts to the spectacularly loose Z band reserved for electrolytics, and choosing the right letter is a circuit-design decision, not a formality.
| Letter | Tolerance | Typical service |
|---|---|---|
| B | ±0.1 pF | Precision RF and resonant circuits |
| C | ±0.25 pF | Tight RF, filters and oscillators |
| D | ±0.5 pF | Matched RF pairs |
| F | ±1% | Timing circuits on film dielectrics |
| G | ±2% | Timing and active filters |
| J | ±5% | Precision-grade general use |
| K | ±10% | The everyday workhorse grade |
| M | ±20% | General-purpose ceramics, decoupling |
| Z | +80% / −20% | Large electrolytics, bulk storage |
Two practical notes. First, tolerance is multiplicative above the absolute codes — a K-band 1 µF part can legitimately measure 1.1 µF brand new, which is exactly why a decoupling network rarely cares. Second, the Z band is deliberately asymmetric because electrolytics are cheapest to manufacture on the high side and the circuits that use them only care that the value is at least a minimum. The converter applies any letter to any decoded value so the real-world range is always visible.
Same parts, four labelling traditionsPhoto: UnsplashWhy the Same Capacitor Reads Differently in Four Places
Unit conventions are cultural artefacts. They predate global supply chains, they survive because the engineers who trained on them keep drawing the schematics, and they guarantee that any engineer working across regions will convert units daily. The four traditions below cover nearly everything you will meet.
The converter is deliberately indifferent to all of them: type the value the way the document in front of you writes it, pick the unit it used, and every other convention appears instantly.
US schematics & service manuals
Skip nanofarads entirely
American practice jumps from pF to µF: 100 nF is drawn as 0.1 µF and 4.7 nF as 4700 pF. Reading a US sheet with a nF habit is the classic factor-of-1000 mistake.
European datasheets & IEC documents
Use nF freely
IEC 60062-writing vendors label 100 nF as 100 nF, keeping every unit in its natural range and the decimal point away from the leading edge.
Old motor & HVAC labels
Write mFD / MFD / mF for µF
'MFD' is literally the abbreviation for microfarad on decades of motor cans. A 30 MFD run cap is 30 µF — never 30 000 µF.
SMD ceramics above ~10 µF
Print the value directly
Beyond roughly 10 µF the multiplier digits get unwieldy, so parts print '10' or '22' with a µF marker. The package family disambiguates what digits cannot.
mF on a Motor Label Means µF — Always
Decades of motor cans, HVAC run capacitors and pump labels abbreviate microfarad as mF, mFD or MFD, because the µ character was beyond their label printers and the abbreviation for "micro farad" got written with the closest available letter. To a modern eye trained on SI prefixes, mF reads as millifarads — a factor of one thousand too large. Trust the context instead of the prefix: a motor run capacitor is never measured in millifarads. A "35 mF" HVAC can is a 35 µF part, full stop.
The reverse trap exists too: modern supercapacitors and some large film caps honestly quote millifarads, and mF there really is 1000 µF. The disambiguator is the component family. Oil-filled motor cans: mF = µF. Anything marked supercap or UL-listed energy storage: mF = 1000 µF. When a label is genuinely ambiguous, the physical size settles it — a matchbox-sized part cannot hold 35 000 µF at 440 V.
Five Conversions You Will Actually Meet
Everything above the arithmetic is one multiplication by a power of ten. Watch the same five values flow through the ladder, and the pattern becomes automatic.
- 1
The decoupling cap: 104
The marking is 104, so two significant digits (10) and four zeros → 100 000 pF. Three places down to nF gives 100 nF; three more to µF gives 0.1 µF. One part, three documents, three notations.
- 2
The timing cap: 4.7 nF
A datasheet says 4.7 nF. Up the ladder: ×1000 → 4700 pF, which codes as 472 (47 × 10²). Down: ÷1000 → 0.0047 µF. On a US schematic the same part reads 4700 pF or 0.0047 µF — never 4.7 nF.
- 3
The coupling cap: 220 nF
European part, European unit. In pF: 220 000, code 224. In µF: 0.22. This is the value that looks wildly different in every tradition and is identical everywhere in the circuit.
- 4
The bulk electrolytic: 1000 µF
Crossing the millifarad boundary is the only time mF is honest on modern parts: 1000 µF = 1 mF. Vendors still write µF because nobody wants a prefix argument on an order form.
- 5
The supercap: 10 F
Ten farads is 10 000 000 µF — the ladder runs out of useful prefixes in the other direction. Above the millifarad rung the farad itself is the readable unit, which is why supercapacitors broke the convention and just quote farads.
Related Calculators
Conversion is the first step of most capacitor work. Once the value is decoded, the main calculator on the home page computes charge and energy for any C and V pair; the series & parallel calculator totals combinations of up to 12 parts; the parallel plate calculator works from geometry instead of markings; and the calculators hub lists every tool in one place. All run live in the browser with nothing sent to a server.
Series & Parallel Capacitors
Combine up to 12 capacitors in series or parallel with per-cap unit selectors. Live total capacitance, the rule behind it and voltage-sharing notes.
Open calculatorParallel Plate Capacitor
Compute capacitance from plate area, separation and dielectric: C = K·ε₀·A/d with 25 real materials, mm²/µm to sq in/mil inputs and fringing warnings.
Open calculatorHVAC Capacitor Under Load
Test an HVAC run capacitor under load: enter amps, volts and 60/50 Hz to get µF = 2652 × A ÷ V, graded good/marginal/replace against the rated value.
Open calculatorCapacitor Energy
Compute energy stored in any capacitor from E = ½CV² with live J/mJ/µJ/nJ/Wh outputs, plus the Q²/(2C) and ½QV forms.
Open calculatorRC Time Constant
Get τ in seconds, ms, µs, ns from any R and C pair, plus the 5τ fully-settled time, charge/discharge curve values and cutoff frequency.
Open calculatorCapacitor Charge
Calculate stored charge Q = CV in C, mC, µC, nC, pC from capacitance and voltage, plus peak displacement current over any R.
Open calculatorCapacitive Reactance
Compute Xc in Ω/kΩ/MΩ from frequency and C, with parallel-R || C and series-R + C impedance, phase angle and admittance.
Open calculatorCapacitor Color Code
Decode 3-band, 4-band and 5-band capacitor color codes to pF/nF/µF with tolerance and voltage, plus a complete reference table.
Open calculatorMotor Capacitor Sizing
Size start and run capacitors for split-phase, cap-start, cap-run and dual-value single-phase motors with HP/voltage inputs and standard ranges.
Open calculatorCrystal Load Cap
Calculate C1 and C2 for a crystal oscillator: C = 2CL − Cstray, with PCB stray cap, transistor input cap and an AT-cut package comparison table.
Open calculatorCoupling & Bypass
Size AC coupling, input/output, emitter and cathode bypass capacitors from impedance and cutoff: C = 1/(2πfR), with an audio stage value table.
Open calculatorRC Filter Cap
Solve C = 1/(2πfR) for low-pass, high-pass, band-pass and notch RC filters, with a live Bode plot, gain readout and an R×C pairs table.
Open calculatorLC Resonance
Get f₀ = 1/(2π√LC) for parallel or series LC tanks, plus Q factor, bandwidth and a capacitor self-resonance (SRF) warning, from any L and C.
Open calculatorPower Supply Cap
Size rectifier bulk, buck-converter output and hold-up capacitors: C = I/(f·ΔV) and C = 2Pt/(V₁²−V₂²), with a ripple and voltage-rating table.
Open calculatorCap Voltage Divider
Split voltage across 2–4 series capacitors instantly: Vn = Q/Cn with equal charge Q = Ceq·Vtotal, plus per-cap bars, charge and rating warnings.
Open calculatorConversion & Codes FAQ
How do I convert pF to µF (and back)?▼
There are one million picofarads in one microfarad, so divide pF by 1 000 000 to reach µF and multiply µF by 1 000 000 to return. The three-digit shortcut: pF to nF is ÷1000, nF to µF is ÷1000 again. So 10 000 pF = 10 nF = 0.01 µF. The converter above keeps all five units on screen so no division is ever done in your head.
What does the code 104 mean on a capacitor?▼
The first two digits are the significant figures in picofarads and the third digit is how many zeros follow: 10 followed by four zeros is 100 000 pF, which is 100 nF or 0.1 µF. One- and two-digit codes read directly in pF (a code '22' is 22 pF), and values below 10 pF use R-notation where the decimal point is written as an R: 4R7 is 4.7 pF. The reverse panel above converts any code both ways.
Why do American schematics skip nanofarads?▼
Tradition and inertia. Nanofarad values were standardised into the SI ladder later than micro and pico, and US drafting practice was already set: values that a European sheet calls 100 nF appear as 0.1 µF, and 4.7 nF appears as 4700 pF. Neither convention is wrong, but mixing them mid-design is how factor-of-1000 errors happen — which is exactly why this converter shows every unit at once.
Is mF the same as µF on my motor capacitor?▼
On modern components, mF honestly means millifarads (1 mF = 1000 µF). On old motor and HVAC labels, mF, mFD and MFD are sloppy period abbreviations for microfarads — a '30 MFD' run cap is 30 µF. Context decides: motor cans never carry millifarad values, so a motor label's mF is always µF. Test that can with the capacitor under load calculator once you have decoded it.
How do I pick the tolerance letter I need?▼
Match the tolerance to what the circuit actually cares about. Timing, filtering and RF tuned circuits deserve F (±1%) or G (±2%) on stable dielectrics. General decoupling and coupling are happy with J (±5%) or K (±10%). Bulk storage and large ceramics accept M (±20%), and Z (+80%/−20%) belongs to electrolytics where the value only needs to be 'at least roughly enough'. Paying for a tighter letter than the circuit needs is wasted money; paying for a looser one in a timing path is a mystery fault waiting to happen.
Why is the farad so absurdly large?▼
Because the farad is defined by charge and voltage, not by practical component size: one farad stores one coulomb at one volt, and a coulomb is an enormous number of electrons. A one-farad capacitor at everyday voltages would be physically huge, which is why every ordinary capacitor is quoted in pF, nF or µF and only supercapacitors — with their microscopic pore-scale electrodes — reach whole farads in a small can.
What code should I print for a value like 4.7 pF?▼
Below 10 pF the 3-digit system cannot express decimals, so the industry switches to R-notation: the decimal point becomes an R. 4.7 pF is marked 4R7, 0.5 pF is marked R50 (or R5 depending on the vendor's house style). The converter's value-to-code panel handles this automatically — type 4.7 pF and it returns 4R7 rather than a wrong multiplier code.
Are MFD, mFD, µF and uF all the same thing?▼
On motor and HVAC equipment, yes — they are all attempts to write microfarad with characters the label printer had: µ became u, or M/mFD. On modern electronic components, mF strictly means millifarads. The rule of thumb: on a motor can or a run capacitor, read every variant as µF; on an electronic component, read mF as 1000 µF. When the label is ambiguous, the part's size and family settle it.
Stop Converting in Your Head
Type the value once — every unit, the closest code and the tolerance range appear before you lift your finger from the keyboard.