Estimate Q values for common fusion reactions fast. Or enter custom masses in seconds easily. Get energy per reaction and exports in one place.
| Reaction | Typical Q-value (MeV) | Energy per reaction (J) | Notes |
|---|---|---|---|
| D + T → He-4 + n | ≈ 17.6 | ≈ 2.82×10-12 | High-yield fusion benchmark. |
| D + He-3 → He-4 + p | ≈ 18.3 | ≈ 2.93×10-12 | Charged products, fewer neutrons. |
| D + D → He-3 + n | ≈ 3.27 | ≈ 5.24×10-13 | One of two main D–D branches. |
| D + D → T + p | ≈ 4.03 | ≈ 6.46×10-13 | Second D–D branch channel. |
The energy released (or required) by a fusion reaction is based on the mass difference between reactants and products.
Fusion reactions convert a small amount of mass into energy. This tool estimates the reaction Q-value from the mass defect Δm and reports energy per reaction in MeV, Joules, and kWh, plus totals for any reaction count.
For a reaction written as reactants → products, the mass defect is Δm = mreactants − mproducts. When Δm is positive, energy is released (exothermic). The energy per reaction follows E = Δm c². Using atomic mass units, a convenient conversion is 1 u ≈ 931.494 MeV/c².
Typical values used in many introductory comparisons include: D–T at about 17.6 MeV (≈ 2.819830876×10-12 J per reaction), D–He-3 at about 18.3 MeV (≈ 2.931983240×10-12 J), D–D (He-3 + n) at about 3.27 MeV (≈ 5.239117593×10-13 J), and D–D (T + p) at about 4.03 MeV (≈ 6.456771835×10-13 J).
Single-reaction energies are tiny, so totals matter. For example, if D–T releases ≈ 2.8198×10-12 J per reaction, then 1020 reactions produce about 2.8198×108 J, which is roughly 78.33 kWh using 1 kWh = 3.6×106 J.
A “mole of reactions” is NA = 6.022×1023 events. At the D–T reference value, that corresponds to about 1.698×1012 J (≈ 471,706 kWh). This highlights why fusion energy density can be extremely high when sufficient reactions occur.
Presets are convenient for quick estimates and comparisons. Custom mode is best when you have specific mass tables, excited-state energies, or reaction products that differ from the preset channels. Enter total reactant and product masses consistently, then let the calculator convert to MeV and Joules.
If Δm becomes negative, the reaction is endothermic in the chosen mass model. This can happen when you enter inconsistent masses, omit emitted particles, or mix nuclear masses with atomic masses incorrectly. Re-check that electrons are treated consistently on both sides.
After calculation, export a CSV for spreadsheets or generate a PDF for sharing. For documentation, record the reaction channel, the mass data source, units, and the number of reactions used for totals. This makes results reproducible and easier to audit later.
It is the Q-value for a single fusion event, computed from mass defect. The calculator reports it in MeV, Joules, and kWh equivalents for easy comparison.
MeV is common in nuclear physics, while Joules and kWh are practical for engineering totals. The conversions help connect reaction-level physics to usable energy scales.
Use one consistent system on both sides. Presets use atomic masses. In custom mode, do not mix atomic and nuclear masses unless you also account for electron masses consistently.
A negative mass defect implies the reaction would require energy input under the provided masses. Check that all products are included and that the mass data matches the reaction channel.
They are good for quick estimates. Exact Q-values can vary slightly with mass datasets, binding energies, and excited states. For precise work, use custom mode with your preferred values.
Enter the reactions count in the form. The calculator multiplies per-reaction energy by that count and reports totals in MeV, Joules, and kWh.
Yes. The PDF button generates a PDF from the result panel, and the CSV download exports the latest computed values stored in the session.
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.