Convert total energy into specific energy instantly here. Choose units, save outputs, and compare scenarios. Fast, accurate calculations for labs, engines, and fluids easily.
Specific energy is energy per unit mass. It is commonly written as: e = E / m
Rearrangements used by this calculator: E = e × m and m = E / e.
| Case | Energy (kJ) | Mass (kg) | Specific energy (kJ/kg) |
|---|---|---|---|
| A | 2500 | 5 | 500 |
| B | 120 | 0.8 | 150 |
| C | 3600 | 12 | 300 |
Tip: Try Case A by selecting “Specific energy (E / m)”.
Energy per unit mass (also called specific energy) tells you how much energy is associated with each kilogram of material. The base unit is J/kg, but engineers often use kJ/kg, MJ/kg, or Wh/kg. Because it normalizes by mass, it is ideal for comparing fuels, batteries, compressed gases, and thermal processes on the same scale.
A fixed energy value has a larger effect on a small mass than on a large mass. For example, 2,500 kJ applied to 5 kg gives 500 kJ/kg, while the same 2,500 kJ applied to 50 kg gives only 50 kJ/kg. This calculator highlights that sensitivity instantly by switching between E, m, and E/m.
Specific energies vary widely. Many hydrocarbon fuels are on the order of tens of MJ/kg, while common rechargeable batteries are typically a few hundred Wh/kg (roughly around 1 MJ/kg). Thermal changes such as heating water can be thousands of J/kg per degree, so “large” or “small” depends heavily on the application.
Electrical and mechanical work are often reported in watt-hours per kilogram. The conversion is direct: 1 Wh/kg = 3600 J/kg and 1 kWh/kg = 3.6 MJ/kg. For a quick check, 250 Wh/kg corresponds to about 0.9 MJ/kg, useful when comparing battery specifications with fuel data.
In mechanics, specific kinetic energy is proportional to the square of speed: ek = v²/2. That means doubling speed increases energy per kilogram by a factor of four. This is one reason transport systems pay close attention to energy per mass when performance targets change.
For temperature change, specific energy can be estimated by e = c·ΔT, where c is specific heat capacity. Water has a high heat capacity, so it requires more energy per kilogram to raise temperature compared with many solids. When you enter energy and mass from experiments, E/m helps you compare runs cleanly.
Choose the unknown (specific energy, energy, or mass), then enter the two known quantities with units. Keep decimal places consistent when you are building a report. If you are comparing scenarios, export CSV to track cases, or export PDF to attach a single calculation to lab notes and design reviews.
The most frequent issues are mixed units (kJ vs J), forgetting that “cal” is not “kcal,” and using grams while interpreting results as kg. Use the output unit selectors to standardize reporting. If your computed value is unexpectedly large, check whether your mass was entered in g or kg and whether the energy unit matches your source data.
Energy is the total amount (J, kJ, kWh). Specific energy is energy divided by mass (J/kg, Wh/kg). Specific energy lets you compare systems fairly when their masses differ.
Use measured values from your source: total energy and mass, or mass and specific energy, etc. Select the correct units, and keep consistent significant figures. The calculator converts everything internally before computing.
It guides you by making the selected “unknown” read-only, so you focus on the two required quantities. The result still shows all three values after calculation.
Multiply Wh/kg by 0.0036 to get MJ/kg. For example, 250 Wh/kg × 0.0036 ≈ 0.9 MJ/kg. Use the unit selectors to verify the conversion.
Yes. If you know energy added and sample mass, the calculator gives E/m, which you can compare across trials. Pair it with c·ΔT analysis when you want a temperature-based interpretation.
Recheck unit choices, especially J vs kJ and g vs kg. Confirm that values are positive and come from the same scenario. Large discrepancies often come from a mass unit mismatch.
Exports include the latest computed energy, mass, and specific energy, plus the selected calculation mode. Add an optional note to label a run, then export for documentation or sharing.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.