Methodology & Sources

Cal Core is an estimation tool, and we think you should be able to see exactly how the estimate is produced. This page documents the formula, the published data behind it, the adjustments we apply, and — just as importantly — what the number cannot tell you.

What Cal Core estimates

Given a calorie amount, your body weight, and an activity, Cal Core estimates how long that activity would take to expend that many calories. It is a "calories out" approximation for a single activity. It is not a diet planner, a medical tool, or a measurement of your actual metabolism.

The formula

Every result comes from the standard MET (Metabolic Equivalent of Task) equation used throughout exercise science:

The constant 3.5 is the assumed resting oxygen uptake in millilitres per kilogram per minute (1 MET), and dividing by 200 converts oxygen consumption into kilocalories. This is the same per-minute energy equation published by the American College of Sports Medicine.

Where our MET values come from

The MET value for each activity is drawn from the Compendium of Physical Activities, the reference dataset that assigns a measured energy cost to hundreds of activities. It is the same source used by researchers, public-health bodies, and most reputable fitness calculators.

Ainsworth BE, Haskell WL, Herrmann SD, et al. 2011 Compendium of Physical Activities: a second update of codes and MET values. Medicine & Science in Sports & Exercise. 2011;43(8):1575–1581.

The fitness-level adjustment

Compendium MET values describe an "average" person. Two people of the same weight can burn energy at noticeably different rates for the same activity, largely because of conditioning and movement efficiency. To reflect this, Cal Core applies an optional multiplier to the base calculation:

• Beginner / less active: ×0.85
• Intermediate: ×1.0 (the unadjusted Compendium value)
• Advanced / very active: ×1.15

These multipliers are a deliberate simplification. They are meant to nudge the estimate in the right direction, not to model your individual physiology precisely.

What the estimate does not account for

A single MET-based number is useful for comparison, but several real factors sit outside it:

• Individual metabolism. Resting metabolic rate varies by roughly 10–15% between people of the same size, age, and sex.
• Body composition. Muscle and fat tissue have different energy costs; two people at the same weight are not metabolically identical.
• Afterburn (EPOC). Intense activity keeps your metabolism elevated for a while afterward — a real effect the per-minute formula ignores.
• Environment and technique. Heat, altitude, incline, wind, and how efficiently you move all shift the true cost.

How accurate is it?

For most people, MET-based estimates land within roughly 10–20% of measured energy expenditure. That makes Cal Core reliable for comparing activities against each other and for building intuition about effort — and unsuitable for precise tracking, where a heart-rate monitor, metabolic cart, or clinical measurement would be appropriate.

Editorial approach

Activity descriptions and guides on this site are written to be accurate and genuinely useful rather than to pad word count. When we describe how an activity burns calories, we base it on established exercise-physiology principles and the Compendium's MET assignments. Where something is an approximation or a rule of thumb, we say so.

Not medical advice

Cal Core is for general information and everyday curiosity. It is not medical, nutritional, or clinical advice, and it should not be used to make decisions about medical conditions, disordered eating, or structured weight management without a qualified professional. See our Disclaimer for details.