Energy equivalents
Physicists measure energy in whatever unit fits: electronvolts for particles, kelvins for thermal energy, hertz or inverse centimetres for spectroscopy, daltons for masses. These factors convert between them through E = mc² = hc/λ = hν = kT. Read across: 1 unit of the row equals the cell's value in the column unit.
Since 2019 every relationship among J, kg, m⁻¹, Hz, K and eV is exact. The atomic mass unit and the hartree are measured, so their rows and columns carry uncertainties.
| 1 … | J | kg | m⁻¹ | Hz | K | eV | u | Eₕ |
|---|---|---|---|---|---|---|---|---|
| J | 1 | 1.112 650 056… × 10−17 | 5.034 116 567… × 1024 | 1.509 190 179… × 1033 | 7.242 970 516… × 1022 | 6.241 509 074… × 1018 | 6.700 535 2471(21) × 109 | 2.293 712 278 3969(25) × 1017 |
| kg | 8.987 551 787… × 1016 | 1 | 4.524 438 335… × 1041 | 1.356 392 489… × 1050 | 6.509 657 260… × 1039 | 5.609 588 603… × 1035 | 6.022 140 7537(19) × 1026 | 2.061 485 788 7415(22) × 1034 |
| m⁻¹ | 1.986 445 857… × 10−25 | 2.210 219 094… × 10−42 | 1 | 299 792 458 | 1.438 776 877… × 10−2 | 1.239 841 984… × 10−6 | 1.331 025 048 24(41) × 10−15 | 4.556 335 252 9132(50) × 10−8 |
| Hz | 6.626 070 15 × 10−34 | 7.372 497 323… × 10−51 | 3.335 640 951… × 10−9 | 1 | 4.799 243 073… × 10−11 | 4.135 667 696… × 10−15 | 4.439 821 6590(14) × 10−24 | 1.519 829 846 0574(17) × 10−16 |
| K | 1.380 649 × 10−23 | 1.536 179 187… × 10−40 | 69.503 480 04… | 2.083 661 912… × 1010 | 1 | 8.617 333 262… × 10−5 | 9.251 087 2884(29) × 10−14 | 3.166 811 563 4564(35) × 10−6 |
| eV | 1.602 176 634 × 10−19 | 1.782 661 921… × 10−36 | 8.065 543 937… × 105 | 2.417 989 242… × 1014 | 1.160 451 812… × 104 | 1 | 1.073 544 100 83(33) × 10−9 | 3.674 932 217 5665(40) × 10−2 |
| u | 1.492 418 087 68(46) × 10−10 | 1.660 539 068 92(52) × 10−27 | 7.513 006 6209(23) × 1014 | 2.252 342 721 85(70) × 1023 | 1.080 954 020 67(34) × 1013 | 9.314 941 0372(29) × 108 | 1 | 3.423 177 6922(11) × 107 |
| Eₕ | 4.359 744 722 2060(48) × 10−18 | 4.850 870 209 5419(53) × 10−35 | 2.194 746 313 6314(24) × 107 | 6.579 683 920 4999(72) × 1015 | 3.157 750 248 0398(34) × 105 | 27.211 386 245 981(30) | 2.921 262 317 97(91) × 10−8 | 1 |
Cells in bold type are exact. Values truncated by NIST end in “…”. Uncertainties in parentheses apply to the last digits.
Quick reference
- 1 eV corresponds to a temperature of 1.160 451 812… × 104 K and a photon frequency of 2.417 989 242… × 1014 Hz.
- Room temperature, 300 K, corresponds to 25.852 meV.
- A photon of wavelength 1 µm carries 1.239 84 eV (from hc = 1239.841 984 eV·nm).
- One atomic mass unit is 9.314 941 0372(29) × 108 eV of rest energy.