How many calories did your last workout actually burn? Not the number on the treadmill display - those overestimate by 15-30%. The real number, calculated from your body weight and the metabolic equivalent of your activity.
And once you know the burn, a harder question follows: did you replace the fluid you lost through sweat? A single hour of moderate running extracts 0.5-1.5 liters of water from your body. Miss that window and the fatigue you blame on overtraining might just be dehydration.
Then there is protein. You tore muscle fibers during that session. Without enough amino acids in the next 24 hours, those fibers rebuild weaker, not stronger. The difference between 1.2 g/kg and 2.2 g/kg of daily protein is the difference between maintaining muscle and actually gaining it.
Three variables. Three calculators. One body that needs all three dialed in.
The MET number your gym does not show you
Every physical activity has a MET value - a Metabolic Equivalent of Task. Sitting is 1.0. Walking at 5 km/h is 3.5. Moderate running at 10 km/h jumps to 10.0. The formula multiplies MET by your weight in kilograms and time in hours:
Calories = MET x weight (kg) x time (h)
A 75 kg person running 30 minutes at moderate pace: 10 x 75 x 0.5 = 375 kcal. The Calories Burned Calculator covers 23 activities from desk sitting to competitive swimming. What makes it useful is the comparison it enables.
Consider these three sessions, all for a 75 kg person, all 30 minutes:
| Activity | MET | Calories burned | Time to burn 500 kcal |
|---|---|---|---|
| Walking (5 km/h) | 3.5 | 131 kcal | 115 min |
| Strength training | 5.0 | 188 kcal | 80 min |
| Moderate running (10 km/h) | 10.0 | 375 kcal | 40 min |
| HIIT / CrossFit | 10.0 | 375 kcal | 40 min |
| Fast running (12+ km/h) | 12.0 | 450 kcal | 33 min |
The table reveals something important: HIIT and moderate running burn identical calories per minute. The difference is sustainability. Most people can run at 10 km/h for 40 minutes. Most people cannot sustain HIIT beyond 25. For pure calorie burn, the activity you can maintain longer wins.
Weight matters too. An 85 kg person doing the same 30-minute run burns 425 kcal - 13% more than the 75 kg person. As you lose weight, your calorie burn drops. That is not a flaw in the formula. Moving less mass simply costs less energy.
The water debt you did not notice
That 375 kcal run cost your body roughly 400-600 ml of water through sweat. Add normal metabolic losses and you are looking at a daily need far above the mythical "8 glasses."
The Water Intake Calculator uses EFSA reference values: 35 ml per kilogram for men, 30 ml per kilogram for women, then adds adjustments for activity level and temperature. A 70 kg male who trains 3 times per week needs 3.0 liters per day - twelve 250 ml glasses.
The signs of chronic mild dehydration are subtle: afternoon headaches, dark urine, fatigue that three espressos cannot fix. The urine test is the simplest diagnostic - pale straw yellow means hydrated, dark amber means drink immediately.
| Profile | Weight | Activity | Daily water | Glasses |
|---|---|---|---|---|
| Sedentary woman | 55 kg | Low | 1.7 L | 7 |
| Office worker, gym 3x/week | 70 kg | Moderate | 3.0 L | 12 |
| Competitive athlete | 85 kg | Very high | 4.5 L | 18 |
| Breastfeeding mother | 65 kg | Low + nursing | 2.7 L | 11 |
One fact most people miss: coffee counts. It is 98% water. The mild diuretic effect of caffeine at normal doses (3-4 cups) is fully offset by the fluid volume. The old dehydration myth has been debunked repeatedly. What does dehydrate you is alcohol - and that matters if your post-workout routine includes a beer.
160 grams - the muscle gain threshold
You ran. You hydrated. Now the third piece: rebuilding the tissue you broke down.
The Protein Intake Calculator applies ISSN guidelines - not the generic RDA of 0.8 g/kg (which is a minimum to avoid deficiency, not an optimum for performance). The multiplier depends on your goal and training intensity:
| Goal | No training | Recreational | Strength 4-5x | Athlete 6-7x |
|---|---|---|---|---|
| Fat loss | 1.8 | 2.0 | 2.2 | 2.4 |
| Maintenance | 1.2 | 1.6 | 1.8 | 2.0 |
| Muscle gain | 1.6 | 1.6 | 2.0 | 2.2 |
An 80 kg male aiming for muscle gain with regular strength training: 80 x 2.0 = 160 g/day. Split across 5 meals, that is 32 grams per meal. In practical terms: a chicken breast has about 31 g per 100 g. So each meal needs roughly 100 g of chicken-equivalent protein - or a scoop of whey (25-30 g) to supplement.
The fat loss column is counterintuitive. Why do you need MORE protein when cutting? Because a calorie deficit signals your body to break down both fat and muscle for energy. High protein intake - 1.8-2.4 g/kg - tells the body to spare muscle and burn fat preferentially. Protein also has the highest thermic effect: your body burns 20-30% of protein calories just digesting them.
For adults over 50, the calculator adds 0.2 g/kg automatically. Anabolic resistance - the reduced ability of aging muscle to use protein for repair - means older adults need more protein per meal to trigger the same muscle protein synthesis response.
How the three numbers connect
Here is the cascade for an 80 kg male training 4 times per week for muscle gain:
1. Exercise: 4 sessions of 45 minutes strength training = roughly 4 x 300 = 1,200 kcal/week burned through exercise
2. Water: baseline 80 x 35 = 2,800 ml + activity bonus 1,000 ml = 3.8 L/day needed
3. Protein: 80 x 2.0 = 160 g/day to fuel muscle protein synthesis
4. Calorie surplus: TDEE + 300 kcal/day, with protein at 160 g (640 kcal from protein alone)
Skip the water and performance drops by 10-20% before you even feel thirsty. Skip the protein and those 1,200 calories of exercise produce maintenance at best, not growth. Skip the exercise and 160 g of protein just becomes expensive urine.
The tools work best as a system, not in isolation.
Tools discussed in this article
- Calories Burned Calculator - MET-based calorie expenditure for 23 activities, from walking to competitive swimming
- Water Intake Calculator - personalized daily water target based on weight, sex, activity level and temperature
- Protein Intake Calculator - ISSN-based protein needs with per-meal breakdown and food source reference
More Health & Fitness tools
- BMI Calculator - Body Mass Index with WHO classification
- BMR & TDEE Calculator - basal metabolic rate and total daily energy expenditure
- Ideal Weight Calculator - target weight from three clinical formulas
- WHR Calculator - waist-to-hip ratio and cardiovascular risk
- Body Fat Calculator - body fat percentage via U.S. Navy method
- One Rep Max Calculator - 1RM estimation with Epley, Brzycki and Lombardi formulas
Check for a specific weight
- Calories burned 70 kg - how much you burn
- Calories burned 90 kg - higher weight
- Water intake 70 kg - daily hydration
- Protein intake 80 kg - daily protein