Fitness Math: 7 Equations You Need To Know To Build Your Dream Body - Phil Hawksworth
9 months ago

Fitness Math: 7 Equations You Need To Know To Build Your Dream Body

In this video and post I lay out the equations you need to know to take control of your body and achieve the results you desire in your fitness – Fitness Math.

I’m forever inundated with questions about what to eat to lose or gain weight, how to work out how many calories people need etc.

Here I lay out the equations you need to know, so you can assess your own training and diet regimes, understand why they work (or don’t work) and what to change to improve results.

Calories Expended > Calories Consumed = Weight Loss

Want to lose weight? You must be consuming less calories than you expend. There are various different ways to do that; manipulating your diet, activity and workouts are just ways to achieve the basic balance of the equation.


Calories Consumed > Calories Expended = Weight Gain

The opposite is true for weight gain. If you want to put weight on, you need to be taking more calories in than you are expending. Whether that is stored as muscle or fat will depend on your diet and training stimulus, but for your weight to go up, you must have additional calories coming in.


Basal Metabolic Rate = 66.5 + ( 13.75 × weight in kg ) + ( 5.003 × height in cm ) – ( 6.755 × age in years )

Your basal metabolic rate (BMR) is how many calories your body uses to sustain itself. Keep your heart pumping, lungs breathing, cells turning over, etc.

This is what you burn, without any activity. If you were in a coma, you would burn this many calories.

BMR is the base you use to work out your daily expenditure, and then how many calories you need to lose or gain weight.

Increasing muscle mass will increase your BMR.

To calculate your BMR you can use this online calculator, rather than doing it manually if you prefer.


Total Daily Energy Expenditure = BMR x 1.2 – 1.8

Total daily energy expenditure (TDEE) is how many calories you expend on a daily basis. It is BMR + activity.

TDEE will depend on how active you are, with totally sedentary (office job, no exercise) at the bottom. Office job, but moderate workouts in the middle. Then manual labour or full time athlete at the top end.

To estimate your TDEE use BMR x 1.2 (for sedentary) up to 1.8 (for highly active). This is an estimate, so you will need to adjust it and work out the right number for you with experience.

You can use this calculator to work out your TDEE.



Not all nutrients are made equal. Below is how many calories are in the different macronutrient groups.

1 Gram Carbohydrate = 4 calories

1 Gram Protein = 4 calories

1 Gram Fat = 9 calories

1 Gram Alchohol = 7 calories

Use this information to create a diet that will work for your goals. When I’m dieting I prefer to eat lower fat, because it allows for more food volume, less hunger and I find it easier to follow.

What works for you might be different, but you should know the basic fitness math behind any plan, so you understand why it works.


BMI = Fuck all, ignore it

Useless measure that tells you nothing, other than that everyone who lifts weight is ‘obese’.


Force = Mass x Acceleration

Strength is developed by force. Force is mass x acceleration. Meaning to increase force you can either use more weight, or move a lighter weight faster.

This is the theory behind Westside Barbell style speed days, and plyometric training. For full strength development you should train all parts of the strength curve.


Total Time Under Tension x Mass = Muscle Growth

Total time under tension, otherwise called volume is what drives muscle growth.

I dislike the term volume, because it is undefined and there are a lot of variables that go into it. Namely;

  • Reps
  • Sets
  • Number of exercise
  • Number of training sessions
  • Tempo (time under tension per set)

You can adjust any one or multiple of these to increase volume, or total time under tension.

To continue to build muscle you need to continually add more time under tension (volume) and /or more mass (weight).


Fitness Math

People love to over complicate things, especially people who want to sell you something. In truth, changing your body is very simple. It’s not always easy – but it is simple.

Follow these basic equations, and do so consistently over extended periods of time, and you will be successful.

Anything that works does so because it abides by the basic laws of physics. There is no shortcut or magic trick to hack the body, just consistently doing the right things leads to the outcomes you desire.

Want to build your dream body? Learn your fitness math.


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