L’energia è la capacità di compiere lavoro.
1 BTU = 778.171 ft·lb 
1 ft·lb = 0.001 BTU 
Esempio: 
Convert 15 Unità termica britannica in Piede-libbra:
15 BTU = 11,672.567 ft·lb 
| Unità termica britannica | Piede-libbra | 
|---|---|
| 0.01 BTU | 7.782 ft·lb | 
| 0.1 BTU | 77.817 ft·lb | 
| 1 BTU | 778.171 ft·lb | 
| 2 BTU | 1,556.342 ft·lb | 
| 3 BTU | 2,334.513 ft·lb | 
| 5 BTU | 3,890.856 ft·lb | 
| 10 BTU | 7,781.711 ft·lb | 
| 20 BTU | 15,563.423 ft·lb | 
| 30 BTU | 23,345.134 ft·lb | 
| 40 BTU | 31,126.846 ft·lb | 
| 50 BTU | 38,908.557 ft·lb | 
| 60 BTU | 46,690.269 ft·lb | 
| 70 BTU | 54,471.98 ft·lb | 
| 80 BTU | 62,253.691 ft·lb | 
| 90 BTU | 70,035.403 ft·lb | 
| 100 BTU | 77,817.114 ft·lb | 
| 250 BTU | 194,542.786 ft·lb | 
| 500 BTU | 389,085.572 ft·lb | 
| 750 BTU | 583,628.358 ft·lb | 
| 1000 BTU | 778,171.144 ft·lb | 
| 10000 BTU | 7,781,711.437 ft·lb | 
| 100000 BTU | 77,817,114.366 ft·lb |