The formula
eV = J × 6.241509074 × 10¹⁸
Where the factor comes from — each unit by its definition, then its size in SI:
1 J is the SI unit of energy.1 eV = e (elementary charge in C, CODATA 2022) × J = 1.602176634 × 10⁻¹⁹ J
Dividing the two SI sizes gives the factor: 6.24150907446 × 10¹⁸ (rounded for display; the underlying ratio is fixed by the definitions). The reverse factor is 1.602176634 × 10⁻¹⁹.
The SI unit of energy is the joule. Food labels use kilocalories, electricity bills kilowatt-hours, heating specs BTU and particle physics electronvolts — the same quantity in five costumes.
Worked examples
- A day's food (2000 kcal): 8,368,000 J = 5.22289 × 10²⁵ eV — 8,368,000 × 6.241509074 × 10¹⁸ = 5.22289 × 10²⁵
- A 1 kW heater run for one hour (1 kWh): 3,600,000 J = 2.24694 × 10²⁵ eV — 3,600,000 × 6.241509074 × 10¹⁸ = 2.24694 × 10²⁵
- Lifting 1 kg through 1 m at standard gravity: 9.80665 J = 6.12083 × 10¹⁹ eV — 9.80665 × 6.241509074 × 10¹⁸ = 6.12083 × 10¹⁹
- A visible-light photon: 3.20435 × 10⁻¹⁹ J = 2 eV — 3.20435 × 10⁻¹⁹ × 6.241509074 × 10¹⁸ = 2
Frequently asked questions
How many electronvolts is 1 J?
1 J = 6.24150907446 × 10¹⁸ eV.
How do I convert electronvolts back to joules?
Divide by 6.24150907446 × 10¹⁸ — or multiply by 1.602176634 × 10⁻¹⁹: 1 eV = 1.602176634 × 10⁻¹⁹ J.