Since power is a measure of the rate at which work is done, the underlying units are those of
work or energy, and that section should be looked at for explanations concerning the
calorie and Btu. In this section the (IT) values have been used.
In this section it is the horsepower which provides confusion. Just
like the calorie, it can take 5 different values, and these are identified as
necessary by the addition of (boiler), (electric), (metric), (UK) and (water).
Unlike the calorie (whose 5 values are reasonably close to each other), the
horsepower has 4 which are close and 1 (boiler) which is considerably different
 it is about 13 times bigger than the others  but it seems to be very little
used.
The S I unit of power is the watt. To change any of these other units of energy or work into their
equivalent values in watts use the operation and conversion factor given. Those marked with # are
exact. Other values are given to an appropriate degree of accuracy.
Btu/hour
x
0.293
071
Btu/minute
x
17.584
267
Btu/second
x
1055.056
calories/hour
x
0.001
163
#
calories/minute
x
0.069
78 #
calories/second
x
4.1868
#
ft
lbforce/minute
x
0.022
597
ft
lbforce/second
x
1.355
82
gigawatts
[GW]
x 1
000
000
000
horsepower
(electric)
x
746
#
horsepower
(metric)
x
735.499
watts
[W]
1
joules/hour
divide
by
3600
#
joules/minute
divide
by
60 #
joules/second
1
kilocalories/hour
x
1.163
kilocalories/minute
x
69.78
kgforce
metres/hour
x
0.002
724
kgforce
metres/minute
x
0.163
444
kilowatts
[kW]
x
1000
#
megawatts
[MW]
x 1
000
000
# 
