calories and watts cannot be converted.
A calorie is a measurement of energy. A watt is a measurement of power. It would be like asking "What is 1000 gallons of gas in miles per hour?" When you buy electricity you buy energy (not power) units called kilowatt-hours. Do not confuse this with kilowatts per hour. Spend some time thinking about power, energy, rate and force. They can be very confusing and are often misused so look for what the author meant to say.
The simple answer is 1 calorie = .001162 watt hours.
1 nutritional calorie (1000 calories (go figure)) = 1.1620 watt hours.
1000 (nutritional) calories (kCal) = 1162 watt-hours.
The inefficient body the conversion is about 20%.
Therefore 1000 kCal =1162 watt-hours * .20 = 232 watts-hour work output.
Detailed
I have a crank generator that has a 100 watt light bulb connected to it. When I am cranking fast enough to get the bulb to full brightness I am putting 100 watts into the bulb. If I do it for one minute I have put 20% or 1.4 kCal into the bulb and 4.6 kCal into making me me very hot. I am burning a total of 6 kCal each minute. This can vary wildly depending on the type of exercise, body weight, room temperature, etc.
From
http://www.livestrong.com/thedailyplate/fitness/exercise/bicycling-stationary-moderate-150-watts/
Calories on a 150 watt bicycle machine for a 145 lb person
1 cal = 4.186 Joules
1 watt = 1 Joule/1sec
keep in mind that food calories (Cal) are really kilocalories (kcal)
1540 watts
210,000,000 watts
132 watts
100wats
0.25 megawatts is 250,000 watts.
Many coffees are 0 calorie.
746 watts.
95,000 watts.
.0001 watts
45 watts
1650 watts.
25000 watts