Every Capacitance Counts. Know the Value Before You Build.
Capacitor Calculator exists for the moment a circuit stops being an idea and starts being a parts list — the value decoded from a marking, the unit converted, the bank combined, the geometry designed, the replacement verified under load. One main calculator at /#calculator, four specialized companions, one published method, and every assumption in plain sight.
One decoding, one defensible valuePhoto: Unsplash4
Specialized calculators — conversion, series/parallel, plate geometry, under-load
1 000
Factor between every step of the unit ladder — pF, nF, µF, mF, F
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Digits in the EIA code that hides every ceramic cap's value
25
Dielectric materials in the plate calculator, air to ceramic
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Accounts, uploads, or paywalls
Why this site exists
The most expensive mistakes in electronics are not skill mistakes — they are arithmetic ones, and they happen before the first part is placed. Read a 104 disc as 104 pF instead of 100 nF and a filter's cutoff moves by three orders of magnitude. Skip nanofarads because your schematic tradition does, and a 0.1 µF bypass becomes 0.1 pF in the hands of whoever reads it next. Trust a ±20% ceramic where a timing circuit needs ±1% film, and the oscillator that was supposed to tick once a second drifts like a cheap watch. And in the motor world, a run capacitor that has drifted from 35 µF to 25 µF looks perfectly fine on the shelf — while the compressor it serves runs hot, draws current, and dies years early.
Meanwhile, most of what the internet offers is fragmented: a decoder without a tolerance table, a converter without the code anchor, a series/parallel form that makes you re-type every value into a new unit, and HVAC tables that never explain the 2652 they multiply by. Capacitors are also the last mass-market component still hiding their value behind a code — resistors got color bands and public charts decades ago, while the 3-digit EIA system, the R-notation, and the tolerance letters remain tribal knowledge passed around forum posts.
We built CapacitorCalculator.com to close that gap with the boring, correct version of the method engineers already use: marking or value → decoded capacitance in every unit → combination or geometry → tolerance band in plain sight → field verification under load. No rules of thumb pretending to be math. No mystery multipliers. The main calculator lives on the homepage at /#calculator, supported by four dedicated tools for unit conversion, series/parallel banks, plate geometry, and HVAC under-load testing. This page is the contract: how the calculators work, what they promise, and the standards the guides around them answer to.
Read the marking, know the partPhoto: UnsplashFrom a marking on a cap to a verified value, in five stops
Every calculation follows the same sequence, and the sequence is public. Because the method never changes, two people entering the same part can compare numbers line by line — and two different answers from the same inputs are mathematically impossible.
Stop 1
Read the Marking
A ceramic disc printed 104, an old part stamped with a tolerance letter, a code copied off a schematic — the decoder turns any 1–3 digit marking back into a real value: two significant digits, a power of ten, and the worked arithmetic shown right beside the result. One- and two-digit codes read directly in picofarads.
Stop 2
Convert the Units
Datasheets from different continents speak five dialects: pF, nF, µF, mF and F, hopping by exactly 1 000 at every step. The capacitance converter keeps all five on screen at once, updating on every keystroke, and translates any value back to its closest 3-digit code — so a schematic's 0.1 µF, a datasheet's 100 nF and a reel marked 104 are visibly the same capacitor.
Stop 3
Combine the Bank
Parallel capacitors add directly; series capacitors combine by reciprocals — the mirror of the resistor rules. The series/parallel calculator applies both rules to up to 12 parts, each with its own unit selector, and returns the bank total live: four 100 nF decoupling caps in parallel, or a series string of caps sharing a high-voltage rail.
Stop 4
Design the Geometry
When the capacitor does not exist yet — two PCB pads, a sensor plate pair, a home-built variable cap — the parallel plate calculator runs C = K·ε₀·A/d on your dimensions, with 25 dielectric materials from vacuum and air through FR-4 and glass to barium titanate, and flags the fringing regime where the ideal formula turns optimistic.
Stop 5
Test Under Load
A run capacitor can measure fine on a bench and still fail inside the condenser, because heat and ripple current change what the part delivers. The under-load calculator uses the field method — amps through the start winding, volts across the terminals, µF = 2652 × A ÷ V at 60 or 50 Hz — and grades the reading against the rated value with the ±5% / ±10% thresholds, ending in a keep-or-replace verdict.
Textbook Formulas, Stated in the Open
- C = Q/V for charge storage, E = ½CV² for energy — computed for any capacitance and voltage pair
- The decode arithmetic printed per keystroke: 104 = 10 × 10⁴ pF = 100 000 pF
- Codes of one or two digits read directly in picofarads — a part marked 47 is 47 pF
- Sub-10-pF R-notation handled: 4R7 = 4.7 pF, with the decimal marked where the R sits
The EIA Code System, Both Directions
- Three-digit codes decoded: 104 → 10 × 10⁴ pF = 100 nF = 0.1 µF
- Reverse conversion: any value in any unit returns its closest 3-digit code
- Rounding honesty: the note says whether the code is exact or how far it sits from your value
- Every tolerance letter B through Z mapped to its ± range, with the min/max band shown beside the result
Units Treated as First-Class Citizens
- pF, nF, µF, mF and F accepted on every input, switchable per field
- Results displayed in the most readable unit plus the raw farads — no 1000× surprises
- The unit ladder hops by exactly 1 000: 22 000 pF = 22 nF = 0.022 µF, kept visible in the chart
- Regional habits — American schematics that skip nanofarads, old labels that write mF for µF — stop being traps
Field-Service Realism
- The under-load tool measures the part hot, at working voltage — the way the HVAC industry actually tests run capacitors
- Verdicts graded with the field thresholds: good within ±5% of the rated µF, marginal to ±10%, replace beyond
- 60 Hz and 50 Hz mains both supported — the 2652 constant becomes 3183 for European and Asian systems
- Discharge and probe-safety guidance sits beside the result, because live testing is real electrical work
Six audiences, one capacitance
A hobbyist sorting an unmarked grab bag, an engineer sizing a decoupling network, a student proving C = K·ε₀·A/d with real numbers, a tech standing in front of a suspect run cap — all want the same fundamental numbers, each in their own unit of decision. These are the people we design for.
Electronics Hobbyists & Makers
You have a bag of unmarked ceramic caps from a starter kit and a breadboard waiting. The decoder tells you what each disc actually is, the tolerance table says how far the real part may sit from its marking, and the value-to-code converter turns the value your schematic calls for into the code to search for — before you order anything.
Electrical & Electronics Engineers
Decoupling networks, timing circuits, charge-storage checks — the calculator handles the routine arithmetic so you can focus on the decisions: which tolerance grade a timing circuit needs, whether the energy in that bulk cap is what the hold-up budget assumes, and what the code on the requisition should actually read.
Engineering & Physics Students
C = Q/V and E = ½CV² are the equations every circuits course starts from, and the parameters module makes them tangible: change the capacitance, change the voltage, watch the charge and energy update in a unit you can feel. Every formula is on the page, every intermediate step visible — and it runs free on the school Chromebooks that block everything else.
Procurement & Inventory Teams
A pick list says 0.1 µF, the distributor's search box wants a code, and the reels in the bin are marked 104. The converter bridges all three dialects in one keystroke, and the tolerance table explains why the ±10% grade on the quote is — or is not — interchangeable with the part the drawing specified.
Audio & Tube-Amp Builders
Coupling caps and filter banks hinge on reading old markings correctly: a 104J is 100 nF at ±5%, not a promise of hi-fi magic, and a value below 10 pF hides behind R-notation. The decoder and tolerance table recover what the part actually guarantees, so substitutions are made on specs instead of folklore.
HVAC & Motor Technicians
A condenser that hums but cools weakly, a 35/5 µF dual run cap with one weak section, a motor that starts slow on cold mornings — the under-load calculator turns a clamp-meter reading and a voltage measurement into a graded µF verdict with the ±5% / ±10% thresholds, so the replace-or-keep call is defensible on the invoice.
The common thread
Every audience above needs the same handful of numbers — the value, the tolerance band, the combination total, the delivered capacitance — and needs them defensible. Not "the forum said so," but here is the marking read per the EIA standard, here is the formula with every term shown, here is the tolerance range and why. That defensibility is what turns a capacitor decision from a guess into a specification — and it is the difference between one parts order and three.
Five decisions a capacitance feeds
The value is never the deliverable — the parts order, the tolerance grade, the circuit plan, the voltage decision, and the service verdict are. Here is where the output goes once the calculator is done with it.
The Parts Order
The decoded value is the order: 100 nF X7R, ±10%, 50 V or better. The decoder and converter together turn any marking or schematic value into a parts-bin-ready specification — right value, right tolerance class, right code to type into the distributor's search box.
The BOM Decision
Value tolerance drives cost: a timing circuit wants F (±1%) film, decoupling is fine at M (±20%) ceramic. Seeing the guaranteed range beside the value makes the grade choice deliberate instead of habitual — and stops you paying precision prices where general-purpose parts do the job.
The Circuit Plan
Series or parallel, and how many: the bank calculator answers the design question before the order goes out — parallel legs to add capacitance and split ripple current, series strings to reach a voltage one part cannot. The total updates as each part is added, so the circuit plan and the shopping list stay the same document.
The Voltage Decision
Two capacitors of half the value in series can ride a rail neither survives alone — but only if the voltage actually divides evenly, which balancing resistors make true on electrolytics. The series/parallel calculator shows the string total, and the guides cover why the sharing rule needs resistors to be trusted.
The Service Call
The measured µF against the rated µF is the verdict the invoice rests on: good within ±5%, marginal to ±10%, replace beyond. The under-load calculator produces that verdict from a clamp-meter reading and a voltage measurement taken while the system runs — the measurement that decides whether the part ships or stays.
Value known, part ordered, board buildingPhoto: UnsplashWhat we promise — and what we don’t
A calculator earns trust by being precise about its own limits. Here is the complete list of both.
The formulas are textbook
Charge Q = C × V, energy E = ½CV², and the decode rule of two significant digits times a power of ten anchored in picofarads. Nothing exotic, no secret sauce — every formula the calculator uses is stated on the page, and a datasheet and a pocket calculator can reproduce any of its results.
Codes follow the EIA standard
The 3-digit system (two significant digits, a power of ten, anchored in picofarads), the R-notation for sub-10-pF values, and the full tolerance letter table from B (±0.1 pF) to Z (+80/−20%) are implemented exactly as published — including the edge cases, like one- and two-digit markings reading directly in pF.
Dielectric data from published sources
The plate calculator's 25 dielectric constants — vacuum and dry air at one end, barium titanate at the other — come from published reference tables, with the typical range shown where a material's K varies by grade. FR-4 is 4.2 in the tool, and the page explains when a specific datasheet may legitimately differ.
Field math matches field practice
The under-load tool embeds the same constant HVAC service literature publishes — 2652 at 60 Hz, 3183 at 50 Hz — and grades results with the ±5% / ±10% thresholds working technicians use on real calls. Field work deserves field math: the tool reproduces what a competent tech computes with a clamp meter, not a lab approximation of it.
Every number is reproducible by hand
The multiplication behind a decode, the 1 000-per-hop unit ladder, the min/max band from a tolerance letter, the charge and energy from C and V — all of it is arithmetic you can redo on paper in under a minute. If a result ever looks wrong, you are one worked example away from checking it yourself.
How the site itself is engineered
The calculators are half the story. The other half is the set of choices behind the page you are reading — why there is no account, no save-project button, and no premium tier.
Private by architecture
Every calculation — code decoding, unit conversion, bank combination, plate geometry, under-load tests — runs as JavaScript in your browser tab. Your markings, your part values, your service readings never transmit anywhere. No accounts, no saved projects, no build history on our side. Privacy here is structural, not promised.
Instant by design
No spinners, no waiting, no 'calculate' button between you and the number. Results update on every keystroke because the math is a handful of equations running on your own device, and the site is statically built, so pages are typically interactive in under two seconds on a phone on a rooftop.
Free, ad-supported, labeled
Every feature is free with no usage caps and no email gate in front of a result. Advertising — clearly separated from calculator output and editorial content — pays the hosting bill. There is no premium tier hiding the useful half of any tool behind a subscription.
Independent on purpose
We sell no components, no test equipment, no plans. We take no commissions from distributors or manufacturers. The calculators exist because they answer real questions with published standards — not because a supplier asked to be listed. When a tolerance class or a reference value is revised, the data updates with it.
Runs in your browser — nothing to install, nothing sentPhoto: UnsplashHow the guides are written
The main calculator is surrounded by guides — on how the formulas and the code system work, the full directory of calculators and when to reach for each, and quick conversions for the values everyone uses. Every one of them answers to the same five rules — and so do we, on this page.
- We show the working — every guide walks through the formula, a worked example, and the edge cases, so you can check the calculation rather than trust it.
- We label uncertainty — where a number depends on your line frequency, your dielectric batch, or your meter's accuracy, we say so; we never present a typical value as if it were a specification for your part.
- We write for the first-time hobbyist and the working technician — the same page serves someone decoding their first 104 disc and someone diagnosing a 45/5 dual run cap, and neither gets talked down to.
- We keep tools and text in lockstep — when a calculator changes (a new dielectric preset, a revised threshold, a new code example), the guides around it are reviewed against the new behavior, not left to drift.
- We update, and we date — content is reviewed against current EIA coding practice and published reference values, and anything that changes materially gets a fresh look at the examples.
Straight answers about the site
Tool-specific questions live in the homepage FAQ. These are the ones about us.
How accurate is the capacitor calculator?
What methodology does the site follow?
Where do the code tables and tolerance ranges come from?
Why does a code like 104 mean 100 nF?
What tolerance should I choose for my circuit?
How does the HVAC under-load calculation work?
Is the site really free?
Who is behind the site?
Can the results be used for engineering drawings or safety certifications?
How can I support the site?
Explore the site
Four specialized calculators extend the main tool into unit conversion, series/parallel banks, plate geometry, and HVAC under-load testing.
Capacitance Converter
Convert capacitance between pF, nF, µF, mF and F live, and translate any value to its closest EIA 3-digit code with the tolerance range shown.
🔗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.
📐Parallel 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.
❄️HVAC 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.
⚡Capacitor 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.
⏱️RC 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.
🔋Capacitor Charge
Calculate stored charge Q = CV in C, mC, µC, nC, pC from capacitance and voltage, plus peak displacement current over any R.
📶Capacitive Reactance
Compute Xc in Ω/kΩ/MΩ from frequency and C, with parallel-R || C and series-R + C impedance, phase angle and admittance.
🎨Capacitor 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.
🔧Motor 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.
💎Crystal 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.
🔊Coupling & Bypass
Size AC coupling, input/output, emitter and cathode bypass capacitors from impedance and cutoff: C = 1/(2πfR), with an audio stage value table.
📉RC 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.
📻LC 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.
🔌Power 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.
⚖️Cap 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.
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Now decode your capacitors
Our capacitor calculators are free, instant, and run entirely in your browser. Start with the main calculator — enter the code printed on the part, pick a tolerance, and get the value in every unit with its guaranteed range; or work in reverse from a value you need to the code you should order.
Open the Capacitor Calculator