Precision
Calculators
Professional-grade tools for capacitor design. Calculate energy storage, convert units, and optimize circuit configurations—all free, no signup required.
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Motor Capacitor Sizing Calculator
Size a start or run capacitor for a single-phase motor from horsepower, voltage and RPM. Includes a quick-reference chart and dual-run cap values.
Energy Storage Calculator
Calculate energy stored in a capacitor using E=½CV². Essential for power supply design, flash circuits, and energy storage applications.
Capacitor Value Calculator
Convert between capacitance units (pF, nF, µF, mF, F) instantly. Calculate series and parallel combinations with visual diagrams.
Series & Parallel Calculator
Calculate total capacitance and safe voltage ratings for capacitor banks. Includes charge balance method for series voltage division.
Cross-Reference Tool
Find equivalent capacitors from different manufacturers. Enter any part number to discover compatible alternatives.
Formula Reference
The six equations behind every calculator on this page, each with its variables and a worked example.
JoulesE = energy (J) · C = capacitance (F) · V = voltage (V)
Example: 1,000 µF at 50 V → ½ × 0.001 × 50² = 1.25 J
CoulombsQ = charge (C) · C = capacitance (F) · V = voltage (V)
Example: 470 µF at 25 V → 0.00047 × 25 = 0.01175 C (11.75 mC)
FaradsTotal capacitance falls; the working voltage rating adds up
Example: Two 100 µF in series → 50 µF, at twice the voltage rating
FaradsCapacitance adds; the rating is that of the lowest-rated unit
Example: 100 µF + 47 µF in parallel → 147 µF
Secondsτ = seconds · R = resistance (Ω) · C = capacitance (F)
Example: 10 kΩ with 100 µF → τ = 1 s, so ~5 s to discharge fully
OhmsXc = reactance (Ω) · f = frequency (Hz) · C = capacitance (F)
Example: 10 µF at 60 Hz → 1 / (2π × 60 × 0.00001) ≈ 265 Ω
Frequently Asked Questions
Which capacitor calculator should I use?
Sizing a start or run capacitor for a single-phase motor: use the motor capacitor sizing calculator. Working out stored energy or discharge time: use the energy storage calculator. Combining capacitors into a bank: use the series and parallel calculator. Converting between pF, nF and µF: use the capacitor value calculator.
How do I calculate energy stored in a capacitor?
Use the formula E = ½CV², where E is energy in Joules, C is capacitance in Farads, and V is voltage in Volts. For example, a 1000µF capacitor charged to 50V stores E = ½ × 0.001 × 50² = 1.25 Joules.
How do capacitors add in series vs parallel?
In parallel, capacitances add directly: C_total = C1 + C2 + C3. In series, reciprocals add: 1/C_total = 1/C1 + 1/C2 + 1/C3. Series connections reduce total capacitance but increase voltage rating.
How do I calculate total capacitance for capacitors in parallel?
Add the values together. Three capacitors of 100µF, 47µF and 22µF in parallel give 169µF. Parallel capacitance always increases, but the voltage rating of the bank is only as high as the lowest-rated capacitor in it, not the sum.
What voltage rating do I need for capacitors in series?
Voltage divides across series capacitors in inverse proportion to capacitance, so the smallest capacitance sees the highest voltage. Identical capacitors share the voltage equally, which is why two matched 100µF 250V units give 50µF at 500V. With mismatched values the smaller unit can be driven past its rating, so series banks are normally built from matched capacitors with balancing resistors across each one.
How do I convert between pF, nF, and µF?
1 µF = 1,000 nF = 1,000,000 pF. To convert: divide by 1000 to go up (pF→nF→µF), multiply by 1000 to go down (µF→nF→pF). Our calculator handles all conversions automatically.
What is the formula for capacitor discharge time?
Discharge time depends on the RC time constant: τ = R × C. A capacitor discharges to ~37% after 1τ, ~14% after 2τ, ~5% after 3τ, and ~2% after 4τ. Full discharge is typically considered 5τ.
Are these capacitor calculators free to use?
Yes, all our capacitor calculators are completely free with no registration required. Use them as many times as you need for your engineering projects.
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