La energía es la capacidad de realizar el trabajo.Existe en varias formas, como cinética, potencial, térmica, etc. Se mide en Joules (J).
1 Wh = 2,655.22 ft·lb 
1 ft·lb = 0 Wh 
Ejemplo: 
Convertir 15 Vatio hora a Libra de pie:
15 Wh = 39,828.296 ft·lb 
| Vatio hora | Libra de pie | 
|---|---|
| 0.01 Wh | 26.552 ft·lb | 
| 0.1 Wh | 265.522 ft·lb | 
| 1 Wh | 2,655.22 ft·lb | 
| 2 Wh | 5,310.439 ft·lb | 
| 3 Wh | 7,965.659 ft·lb | 
| 5 Wh | 13,276.099 ft·lb | 
| 10 Wh | 26,552.197 ft·lb | 
| 20 Wh | 53,104.394 ft·lb | 
| 30 Wh | 79,656.592 ft·lb | 
| 40 Wh | 106,208.789 ft·lb | 
| 50 Wh | 132,760.986 ft·lb | 
| 60 Wh | 159,313.183 ft·lb | 
| 70 Wh | 185,865.38 ft·lb | 
| 80 Wh | 212,417.578 ft·lb | 
| 90 Wh | 238,969.775 ft·lb | 
| 100 Wh | 265,521.972 ft·lb | 
| 250 Wh | 663,804.93 ft·lb | 
| 500 Wh | 1,327,609.86 ft·lb | 
| 750 Wh | 1,991,414.79 ft·lb | 
| 1000 Wh | 2,655,219.719 ft·lb | 
| 10000 Wh | 26,552,197.194 ft·lb | 
| 100000 Wh | 265,521,971.943 ft·lb |