In those contexts, the unit of specific heat capacity is BTU/lb⋅°R, or 1 ⁠ BTU / lb⋅°R ⁠ = 4186.68 ⁠ J / kg⋅K ⁠. The BTU was originally defined so that the average specific heat capacity of water would be 1 BTU/lb⋅°F. Note the value's similarity to that of the calorie - 4187 J/kg⋅°C ≈ 4184 J/kg⋅°C (~.07%) - as they are essentially measuring the same energy, using water as a basis reference, scaled to their systems' respective lbs and °F, or kg and °C.