Guides
14 explanations of what sits behind the calculators — where each equation came from, what it assumes, and how much confidence its output deserves.
- How 1RM formulas differ, and when each is most accurate
Five published equations estimate your one rep max from a set. Where they agree, where they diverge, and why the spread between them is the useful signal.
6 minute read
- How BMR is calculated, and why the equations disagree
What basal metabolic rate actually measures, how the prediction equations were built, and why three of them give different answers for the same person.
6 minute read
- How body fat measurement methods compare on accuracy
DXA, hydrostatic weighing, calipers, tape measures and smart scales, ranked by how much they actually measure and what each one gets wrong.
7 minute read
- How the US Navy body fat method works
Why a tape measure around your neck and waist predicts body fat, where the logarithms come from, how to measure correctly, and when it misreads.
6 minute read
- How to build a calorie target that is sustainable
Why the size of a deficit matters less than whether you can hold it, how to choose one you can live with, and what the safety limits on this site are for.
6 minute read
- How to read a pace chart
Converting between pace, speed and finish time, why race projections at constant pace are wrong, and what Riegel's formula does about it.
5 minute read
- How to set a protein target
The RDA answers a different question from the one most people ask. What the evidence supports for training, when higher intakes help, and how to scale it.
6 minute read
- MET values explained
What a metabolic equivalent is, where the Compendium values come from, why two calculators disagree on the same workout, and how far to trust them.
6 minute read
- Mifflin-St Jeor vs Harris-Benedict vs Katch-McArdle
Three BMR equations, three different answers for the same person. Which is most accurate, when, and why the best one on paper is often the worst in practice.
6 minute read
- The maintenance calories misconception
Maintenance is not a fixed number you can look up. It moves with your weight, activity and intake — which changes how you should use a calorie calculator.
6 minute read
- Understanding heart rate zones
Where the zone model comes from, why Karvonen beats a flat percentage of maximum, and why "220 minus age" is far less reliable than it looks.
6 minute read
- What TDEE activity multipliers actually mean
The 1.2 to 1.9 multipliers every calculator uses come from no published paper. Where they came from, what the research says, and how to choose one.
7 minute read
- Why BMI is a screening tool, not a diagnosis
BMI was designed to describe populations, not people. What it can tell you, what it structurally cannot, and why it still appears on every health form.
6 minute read
- Why scale weight fluctuates day to day
Two kilograms of overnight change is water, glycogen and gut contents, not fat. What actually moves the number, and how to read a trend through the noise.
5 minute read