How powerful should be heated clothes? How many watts of heat needed to ride a motorcycle in the winter? Is there enough 10 Watt heated blanket for me? All these questions can be answered if you know some basic information about yourself.

Met - Metabolic Rate
The Met is often used as a measuring unit of human body heat or power production
The metabolic rate, or human body heat or power production, is often measured in the unit "Met". The metabolic rate of a relaxed seated person is one (1) Met, where

1 Met = 58 W/m2

The mean surface area of the human body is approximately 1.8 m2 (19.4 ft2).  The total  metabolic heat for a mean body can be calculated by multiplying with the area. The total heat from a relaxed seated person with mean surface area would be

58 W/m2 x 1.8 m2 = 104 W

Typical metabolic rates for some common activities are indicated in the table below:

 

Activity W Met
Reclining
Sleeping
 83 0.8
Seated relaxed 104 1.0
Standing at rest 126 1.2
Sedentary activity (office, dwelling,
school, laboratory)		 126 1.2
Car driving 144 1.4
Graphic profession - Book Binder 153 1.5
Standing, light activity (shopping, laboratory, light industry) 167 1.6
Teacher 171 1.6
Domestic work -shaving, washing and dressing 180 1.7
Walking on the level, 2 km/h 198 1.9
Standing, medium activity (shop assistant,
domestic work)		 209 2.0
Building industry - Brick laying (Block of 15.3 kg) 225 2.2
Washing dishes standing 261 2.5
Domestic work - raking leaves on the lawn 306 2.9
Domestic work - washing by hand and ironing (120-220 W) 306 2.9
Iron and steel - ramming the mould with a
pneumatic hammer		 315 3.0
Building industry -forming the mould 324 3.1
Walking on the level, 5 km/h 360 3.4
Forestry -cutting across the grain with a
one-man power saw		 369 3.5
Volleyball
Bicycling (15 km/h)
 418 4.0
Calisthenics 470 4.5
Building industry - loading a wheelbarrow with stones and mortar
 495 4.7
Golf
Softball
 522 5.0
Gymnastics
 574 5.5
Aerobic Dancing
Swimming
 624 6.0
Sports - Ice skating, 18 km/h
Bicycling (20 km/h)
 648 6.2
Agriculture - digging with a spade (24 lifts/min.)
 674 6.5
Skiing on level, good snow, 9 km/h
Backpacking
Skating ice or roller
Basketball
Tennis
 729 7.0
Handball
Hockey
Racquetball
Cross County Skiing
Soccer
 835 8.0
Running 12 min/mile
Forestry - working with an axe (weight 2 kg. 33 blows/min.)
 900 8.5
Sports - Running in 15 km/h
 990 9.5

As the table shows, our body can work real miracles. We can produce as much heat as an electric iron, or switch to power saving mode. We can get very hot under heavy physical activity, but at rest we may need an external heater.

The metabolic rates varies from person to person and the intensity of the activity. Maximum capacity: 20 met - healthy man at age 20; but only 7 met - at age 70. Maximum rate for women is up to 30% lower than for man.

Moreover, the metabolism is greatly reduced with age, i.e. an elderly person in the same physical activity may need more external heat.

 

Now let's think about our clothes.