A horsepower-hour (hph) is an outdated unit of energy, not used in the SI system of units. The unit represents an amount of work a horse is supposed capable of delivering during an hour (1 (one) horsepower integrated over a time interval of an hour). Based on differences in the definition of what constitutes the 'power of a horse', a horsepower-hour differs slightly from the German "Pferdestärkenstunde" (PSh):
| Definition | Relation to SI units |
|---|---|
≡ 1 hp × 1 h |
| quad | gallon-atmosphere (imperial) | terajoule | foot-poundal | yottajoule | horsepower-hour | gallon-atmosphere (US) | gigajoule |
|---|---|---|---|---|---|---|---|
| 1 | 2.290449966093 × 1015 | 1,055,055.85262 | 2.5036855629267 × 1019 | 1.05505585262 × 10-6 | 393,014,778,922.23 | 2.750715716152 × 1015 | 1,055,055,852.62 |
| 4.3659543530906 × 10-16 | 1 | 4.6063256925 × 10-10 | 10,930.9768822 | 4.6063256925 × 10-22 | 0.0001716 | 1.2009499 | 4.6063256925 × 10-7 |
| 9.4781712031332 × 10-7 | 2,170,927,691.084 | 1 | 23 730 360 404 232 | 1.0 × 10-12 | 372,506.1359986 | 2,607,175,448.8838 | 1 000 |
| 3.9941117798796 × 10-20 | 9.148313190797 × 10-5 | 4.2140110093805 × 10-14 | 1 | 4.2140110093805 × 10-26 | 1.5697449581601 × 10-8 | 0.0001099 | 4.2140110093805 × 10-11 |
| 947,817.1203133 | 2.170927691084 × 1021 | 1 000 000 000 000 | 2.3730360404232 × 1025 | 1 | 3.7250613599864 × 1017 | 2.6071754488838 × 1021 | 1.0 × 1015 |
| 2.5444335776439 × 10-12 | 5,827.8978016 | 2.684519537696 × 10-6 | 63,704,616.141728 | 2.684519537696 × 10-18 | 1 | 6,999.0134307 | 0.0026845 |
| 3.6354174810871 × 10-16 | 0.8326742 | 3.835568490138 × 10-10 | 9,101.9422626 | 3.835568490138 × 10-22 | 0.0001429 | 1 | 3.835568490138 × 10-7 |
| 9.4781712031332 × 10-10 | 2,170,927.691084 | 0.001 | 23,730,360,404.232 | 1.0 × 10-15 | 372.5061360 | 2,607,175.4488838 | 1 |
| Symbol | Definition |
|---|---|
| ≡ | exactly equal |
| ≈ | approximately equal to |
| = | equal to |
| digits | indicates that digits repeat infinitely (e.g. 8.294 369 corresponds to 8.294 369 369 369 369 …) |
| 1 horsepower-hours | = 2684519.537696 joules |
| 2 horsepower-hours | = 5369039.075392 joules |
| 3 horsepower-hours | = 8053558.613088 joules |
| 4 horsepower-hours | = 10738078.150784 joules |
| 5 horsepower-hours | = 13422597.68848 joules |