Bodypump workouts aren't the only thing you're doing all day right?
You walking around your home consumes calories.
You cleaning your house consumes calories.
You sitting on the computer typing out a question consumes calories.
You sleeping consumes calories.
A "calorie" is a unit of measurement for energy similar to how a "kilometer" is a unit of measurement for distance. In this case, it's the amount of energy that is required to raise 1 gram of water by 1 degree Celsius. Food, muscle, glycogen, and body fat hold calories. Moving and living uses calories. All of these are rated in "kilocalories" or "kcal" or sometimes with a big "C". When people mention a "calorie", it's almost always referring to a "kilocalorie". The Bodypump is actually claiming it burns 600 kilocalories which is 33% of the total 1800 kcal consumed (Bodypump is also probably greatly exaggerating the number just fyi).
The biggest consumption of calories for most people is the "Resting Metabolic Rate" which is the amount of calories you use to "just survive". Breathing, thinking, heart beating, and so on. The things your body needs to do in order to continue living.
The second biggest consumption is your NEAT or "Non-Exercise Activity Thermogenesis". These include activities that you do throughout the day. These include cleaning, typing, walking, talking, writing, shopping, and much, much more.
The third biggest consumption is exercise. As you have seen, it's not actually as much as you would think. Although it does help significantly.
The fourth biggest consumption is the Thermogenic Effect of Food which is how much energy it takes to digest the food you consume.
All four of these things combined make your Total Daily Energy Expenditure which is your TDEE. If you eat equivalent to your TDEE, then you will not gain or lose weight. If you eat above it, you will gain weight. If you eat below it, you will lose weight.
*Note: This distribution is different for everyone so don't think this is set in stone. It's just an example.
If you would like an estimate of what your BMR/RMR is, there are a variety of calculators on the web.
This website mentions three of the most popular ones: Mifflin-St Jeor Equation, Harris-Benedict Equation, and Katch-McArdle Formula. Each are described respectively as:
Mifflin-St Jeor Equation:
BMR = 10 x <weight_in_kg> + 6.25 x <height_in_cm> - 5 x <age> + 5
BMR = 10 x <weight_in_kg> + 6.25H - 5A - 161
Revised Harris-Benedict Equation:
BMR = 13.397 x <weight_in_kg> + 4.799H - 5.677A + 88.362
BMR = 9.247 x <weight_in_kg> + 3.098H - 4.330A + 447.593
370 + 21.6 x (1 - <bodyfat_percentage>) x <weight_in_kg>
And then to estimate your TDEE, you'd multiply the BMR with a coefficient that depends on your activity level.
- Sedentary (little to no exercise):
TDEE = BMR x 1.2
- Lightly active (light activity or sports 1-3 times a week):
TDEE = BMR x 1.35
- Moderately active (moderate activity or sports 3-5 times a week):
TDEE = BMR x 1.5
- Very active (high activity or sports 5-7 times a week):
TDEE = BMR x 1.7
- Professional athlete (Physically demanding activity is your job):
TDEE = BMR x 1.9
Though it should be stressed that these are estimates and your actual TDEE is going to be different.