Calculator Inputs
Choose a mode, enter engineering values, then calculate. Results appear above this form after submission.
Example Data Table
| Capacitance | Voltage | Stored Energy | Charge | Typical Use |
|---|---|---|---|---|
| 100 µF | 5 V | 1.25 mJ | 500 µC | Small sensor hold-up |
| 470 µF | 12 V | 33.84 mJ | 5.64 mC | Filtering low-power rails |
| 2200 µF | 24 V | 633.60 mJ | 52.80 mC | Controller bulk storage |
| 10 mF | 5.5 V | 151.25 mJ | 55.00 mC | Memory backup support |
| 1 F | 2.7 V | 3.645 J | 2.700 C | Supercapacitor pulse buffer |
Formula Used
Stored Energy
E = 0.5 × C × V²
Energy grows linearly with capacitance and quadratically with voltage. Doubling voltage increases stored energy by four times.
Stored Charge
Q = C × V
Charge represents how much electric charge the capacitor holds at a selected voltage.
Required Capacitance
C = 2E / V²
Use this when the target energy and working voltage are known, and you need the capacitor size.
Required Voltage
V = √(2E / C)
Use this when the capacitor is fixed and the energy target must still be met.
RC Discharge
V(t) = V₀ × e-t / RC
E(t) = 0.5 × C × V(t)²
The discharge profile depends on resistance and capacitance. The time constant is τ = R × C.
Capacitive Reactance
Xc = 1 / (2πfC)
This shows how strongly the capacitor resists alternating current at a selected frequency.
How to Use This Calculator
Pick stored energy, required capacitance, required voltage, or discharge snapshot based on your design question.
Fill the visible fields only. The calculator converts units internally before solving the equations.
Resistance, ESR, tolerance, frequency, and voltage rating give deeper engineering context and safety insight.
The result section appears above the form, directly under the header, with computed values and a graph.
Use the CSV and PDF buttons to save the current result or the example reference table.
FAQs
1. Why does energy rise so quickly with voltage?
Because voltage is squared in the energy formula. A modest increase in voltage creates a much larger increase in stored energy than the same percentage increase in capacitance.
2. What unit should I use for capacitance?
Use the unit printed on your component or datasheet. The calculator accepts farads, millifarads, microfarads, nanofarads, and picofarads and converts them automatically.
3. What does the time constant mean?
The time constant, τ = RC, describes discharge speed. After one time constant, voltage falls to about 36.8% of its starting value during a simple resistive discharge.
4. Why include ESR in the calculator?
ESR helps estimate internal stress, heating, and current limits. It is especially useful for pulse discharge, filtering, and power electronics design reviews.
5. Is the result safe to use directly in hardware?
Use it as an engineering estimate, not a final certification. Always compare with datasheets, derating rules, thermal limits, surge ratings, and application-specific standards.
6. Why can required capacitance drop at higher voltage?
For the same target energy, higher working voltage reduces the needed capacitance because energy depends on voltage squared. That tradeoff often guides storage design choices.
7. What does capacitive reactance tell me?
Reactance indicates how much the capacitor opposes alternating current at a given frequency. Lower reactance means stronger AC coupling or filtering action.
8. Can I use this for supercapacitors?
Yes. The same core formulas apply. For supercapacitors, pay extra attention to ESR, leakage current, balancing, voltage rating, and cycle-life limits.