Energy Density Calculator
Calculate volumetric and gravimetric energy density, battery specific energy, electric/magnetic field energy density, capacitor energy and laser fluence. Separate modes prevent “energy density” from pretending it is one formula across every branch of physics.
Enter your values
Energy Density Calculator chart
The graph updates from the calculator result so you can compare the answer visually instead of staring at one lonely number like civilization intended.
Key terms
Volumetric energy density
Energy per unit volume, e.g. J/m³ or Wh/L.
Gravimetric energy density
Energy per unit mass, commonly called specific energy, e.g. Wh/kg.
Power density
Power per unit mass, area or volume; different from energy density.
Fluence
Pulse energy per unit area, often J/cm² for lasers.
General energy density formulas
The two broad storage metrics are:
Volumetric: u=E/VGravimetric: e=E/mThey answer different questions: how much energy fits in a volume versus how much energy is stored per unit mass.
How to use the energy density calculator
Choose a mode matching the physical problem. Battery mode uses stored energy with mass and/or volume. Field modes use electric or magnetic field quantities. Laser mode calculates energy per illuminated area.
Battery energy density
Battery specifications commonly quote Wh/kg and Wh/L. Cell-level values are usually better than pack-level values because a pack includes enclosure, cooling, busbars, electronics and structural hardware. Compare values only when the measurement basis is similar.
Lithium-ion battery calculation
If a cell stores E watt-hours and has mass m kilograms, specific energy is E/m Wh/kg. If its external volume is V litres, volumetric energy density is E/V Wh/L. Nominal voltage × capacity is a common energy estimate, but real usable energy depends on discharge conditions and limits.
Electric and magnetic field energy
For a linear dielectric, electric-field energy density is proportional to permittivity and E². Magnetic-field energy density depends on permeability and B². The calculator exposes these as separate modes because mixing them into battery Wh/kg would be dimensional chaos.
Capacitor and supercapacitor energy density
Stored capacitor energy is E=½CV². Device-level energy density then divides stored energy by mass or volume. Material-level electric-field energy density uses the field relationship instead. Specify which basis you mean.
Laser pulse energy density and fluence
Laser fluence is pulse energy divided by illuminated area. Spot diameter, beam profile and pulse shape can matter for real processes. A top-hat circular spot estimate is not automatically equivalent to peak fluence in a Gaussian beam.
Power density vs energy density
Energy density describes capacity. Power density describes how quickly energy can be delivered relative to mass, volume or area. A technology can have high energy density and modest power density, or the opposite.
Energy density units
Common units include J/m³, J/L, Wh/L, kWh/m³, J/kg and Wh/kg. Convert energy and the denominator separately before comparing values from different sources.
Worked energy-density examples
Battery
A 60 Wh cell with mass 0.30 kg has 200 Wh/kg specific energy. If the cell volume is 0.25 L, volumetric energy density is 240 Wh/L.
Laser
A 1 J pulse spread uniformly over 1 cm² has fluence of 1 J/cm².
Energy-density unit conversions
1 Wh = 3600 J. Therefore 1 Wh/L equals 3.6 MJ/m³. When comparing battery or fuel values, confirm whether the source uses lower/heating value, usable energy, nominal energy or a full-system basis.
Comparing technologies fairly
A chart comparing batteries, fuels and fields can be misleading unless the denominator and system boundary are the same. Cell chemistry values, battery-pack values and complete vehicle-system values are not interchangeable. DensityCalcs labels the basis rather than ranking mismatched numbers as if they were a horse race.
Frequently asked questions
How do I calculate energy density?
Divide energy by volume for volumetric energy density or by mass for gravimetric specific energy.
What is the formula for energy density?
It depends on the domain. General storage metrics are E/V and E/m; field energy has different equations.
How do I calculate power density?
Divide power by the chosen mass, area or volume basis.
What is the difference between power density and energy density?
Energy density measures stored energy per unit; power density measures rate of energy transfer per unit.
How is battery energy density calculated?
Use stored energy divided by cell or pack mass for Wh/kg, or divided by external volume for Wh/L.
Sources & references
We prefer standards bodies, government/scientific agencies and primary technical references. Reference values can vary with conditions, grade, composition or measurement method.
Related calculators & guides
DensityCalcs · [email protected]