☢️ Mass–Energy Calculator (E = mc²)
Convert between mass and energy with E = mc² — enter a mass to get its energy, or an energy to get its mass.
Energy E
89875500000000 J (5.610e+32 eV)
Mass–energy equivalence: E = m·c², with c = 299,792,458 m/s (exact). Energy also shown in eV. 🔒 Computed in your browser.
How the mass–energy calculator (e = mc²) works
Einstein’s mass–energy equivalence: E = mc², with c = 299,792,458 m/s (exact). A tiny mass corresponds to an enormous energy because c² is huge. Enter mass or energy and the tool gives the other, in joules and electronvolts.
One gram of mass equals about 9×10¹³ J — the energy released in nuclear reactions comes from converting a small fraction of mass. c is an exact defined constant.
Frequently asked questions
What does E = mc² mean?
Mass and energy are equivalent: a mass m has an energy E = mc², where c is the speed of light. Because c² ≈ 9×10¹⁶, even a small mass holds a vast amount of energy.
How much energy is in 1 gram of mass?
E = mc² = 0.001 × (3×10⁸)² ≈ 9×10¹³ J — roughly the energy of a large nuclear explosion. Enter 0.001 kg to see the exact value.
Where does nuclear energy come from?
A small amount of mass is converted to energy in fission and fusion; the “mass defect” times c² gives the energy released.
What is the value of c?
The speed of light, exactly 299,792,458 m/s by definition of the metre.
Can energy turn into mass?
Yes — in particle physics, sufficiently energetic collisions create particles (mass) from energy, the reverse of E = mc².