LabCanvas
Sign inStart free
FeaturesTemplatesGalleryPricingBlogDashboard

Supercapacitor specific capacitance, energy density and battery C-rate calculator

Specific capacitance from a galvanostatic discharge is C = I·Δt / (m·ΔV), with I the current, Δt the discharge time, m the active mass and ΔV the voltage window without the IR drop; from a cyclic voltammogram it is C = ∮I dV / (2·m·v·ΔV) at scan rate v. For a two-electrode cell the energy density is E = ½·C·ΔV² and the power density P = E / Δt; for a battery, the current at n C is n × the capacity and a full charge or discharge takes 1/n hours.

Last updated

FreeNo sign-upRuns in your browserData analysis

Loading Supercapacitor & battery calculator…

At a glance

Supercapacitor & battery calculator at a glance
GCDC = I·Δt / (m·ΔV), ΔV without the IR drop
CVC = ∮I dV / (2·m·v·ΔV), whole loop
Cell vs electrodeSymmetric cell: per-electrode value = 4 × cell value per total mass
Energy, powerE = ½·C·ΔV² (Wh/kg), P = E / Δt (W/kg); two-electrode cells only
BatteryCurrent = C-rate × capacity; time = 1 / C-rate hours
OutputF/g, mF/cm², Wh/kg, W/kg, µWh/cm²; CSV, curve (PNG, SVG)
Runs inYour web browser; nothing is uploaded
PriceFree, no account needed

What it does

  • Specific capacitance from GCD (with IR drop) or CV (loop area or pasted loop)

  • Two-electrode cell or three-electrode single electrode, kept separate

  • Per-electrode value of a symmetric cell (4 × the cell value)

  • Energy density (Wh/kg) and power density (W/kg), gravimetric and areal

  • Battery C-rate ↔ current ↔ time from capacity or specific capacity × mass

  • Plots a pasted discharge curve or CV loop (PNG, SVG) and exports CSV

How to use the supercapacitor & battery calculator

  1. Pick the measurementChoose charge–discharge (GCD), cyclic voltammetry (CV) or battery C-rate.
  2. Say what was measuredTwo-electrode cell (enter the mass of both electrodes) or three-electrode single electrode (enter the working electrode’s mass). Add the electrode area for areal values.
  3. Enter the curveGCD: discharge current, discharge time, voltage window and IR drop, or paste the discharge curve. CV: scan rate and the loop area and window, or paste the whole loop.
  4. Read the resultsGet the capacitance in F/g (and per electrode for a symmetric cell), energy and power density for a cell, and copy or download them.

How it works

C = I·Δt / (m·ΔV)    C = ∮I dV / (2·m·v·ΔV)    E = ½·C·ΔV²    P = E / Δt

Galvanostatic charge–discharge. The gravimetric specific capacitance is C = I·Δt / (m·ΔV), with I the discharge current, Δt the discharge time, m the mass of active material and ΔV the potential window during discharge, excluding the initial IR drop (Idris, Mamba & Xolile 2026, RSC Adv). GCD is the method closest to how a device is used.

Cyclic voltammetry. The capacitance comes from integrating the current over the CV loop with the scan rate v, the mass and the window (Idris et al. 2026). The tool uses the whole closed loop: each sweep passes a charge Q = ∫I dt = ∫I dV / v, the loop contains both the charging and the discharging sweep, and C = Q / ΔV, so C = ∮I dV / (2·m·v·ΔV). CV and GCD values for the same material often differ, because of scan rate, current density and resistance.

Two-electrode or three-electrode. A three-electrode measurement gives one electrode against a reference. In a two-electrode cell the two electrodes act as capacitors in series, so a symmetric cell’s capacitance per total mass is about one quarter of a single electrode’s (Idris et al. 2026). The tool reports the cell value and, for a symmetric cell, the per-electrode value 4 × Ccell. It always says which one it reports.

Energy and power. Energy density is half the capacitance times the square of the voltage, E = ½·C·ΔV², and the average power density is the energy divided by the discharge time (Idris et al. 2026). The tool computes them only for a two-electrode cell, from the cell capacitance per total mass and the same ΔV (after the IR drop), and converts 1 J/g to 1/3.6 Wh/kg. For CV, Δt is one sweep, ΔV / v.

Battery C-rate. At a rate of n C the current is n × the capacity and a full charge or discharge takes 1/n hours: 1 C of a 1.9 mAh cm⁻² electrode is 1.9 mA cm⁻² and 6 C about 11.4 mA cm⁻² (Adv Sci 2024), and 10 C takes 6 minutes (Research 2026).

Worked example: a symmetric two-electrode cell

A symmetric cell with 2 mg of active material in total is discharged at 1 mA from 1.0 V; the IR drop is 0.05 V and the discharge takes 100 s.

  1. ΔV = 1.0 − 0.05 = 0.95 V.
  2. C = 0.001 A × 100 s / 0.95 V = 0.1053 F, so Ccell = 0.1053 F / 0.002 g = 52.6 F/g.
  3. Per electrode: 4 × 52.6 = 210.5 F/g.
  4. E = ½ × 52.6 × 0.95² J/g = 23.75 J/g = 6.60 Wh/kg.
  5. P = 6.60 Wh/kg × 3600 / 100 s = 237.5 W/kg.

Battery: a 2,500 mAh cell at 0.5 C needs 1,250 mA and takes 2 h to charge or discharge fully.

Frequently asked questions

How do you calculate specific capacitance from a charge–discharge curve?

Use C = I·Δt / (m·ΔV): discharge current times discharge time, divided by the active mass and the voltage window. Take the IR drop off the window first.

How do you calculate specific capacitance from a CV curve?

Integrate the current over the voltage for the whole loop and divide by twice the mass, the scan rate and the window: C = ∮I dV / (2·m·v·ΔV). The factor 2 is there because the loop contains both the charging and the discharging sweep.

Why is the capacitance lower in a two-electrode cell than in a three-electrode test?

In a cell the two electrodes are in series, so for a symmetric cell the capacitance per total mass is about a quarter of a single electrode’s. Higher mass loading, resistance and ion transport in a real cell lower it further.

Should I subtract the IR drop?

Yes. The sudden voltage drop at the start of a discharge comes from internal resistance, not stored charge, so the voltage window used for capacitance excludes it.

How is energy density calculated for a supercapacitor?

E = ½·C·ΔV², with C the cell capacitance per total mass and ΔV the voltage window. In F/g and V this gives J/g; divide by 3.6 for Wh/kg. Power density is E divided by the discharge time.

What is C-rate?

The charge or discharge current relative to the capacity: at 1 C a full charge or discharge takes one hour, at 2 C 30 minutes and at C/10 ten hours. The current is the C-rate times the capacity.

What is the difference between F/g and mAh/g?

F/g (specific capacitance) suits capacitive, double-layer storage; mAh/g (specific capacity) suits battery-type, faradaic materials. They are related by Q = C·ΔV, so a conversion depends on the voltage window.

Make the whole figure in LabCanvas

Vector figure editor, slides, 3D models, protein structures and Prism-style graphs, in your browser.

Get started