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Many “calories burned” calculators use the same basic method: select a standardized activity-intensity value, combine it with body mass and time, then convert the result into an estimated calorie total. That explains why different calculators can agree without proving that they use identical code—or that the result is an exact measurement of your personal energy use.
What formula are the calculators using?
A common method uses METs, or metabolic equivalents. One MET is defined as 3.5 milliliters of oxygen per kilogram of body mass per minute and is approximately 1 kilocalorie per kilogram per hour.
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A commonly used conversion estimates calories per minute like this:
kcal/min = MET × 3.5 × body mass (kg) ÷ 200
Multiply that rate by the activity duration in minutes to estimate the session total. For example, the calculation depends on the chosen MET value, your body mass in kilograms, and how long you performed the activity. It is an estimate based on a standardized activity value, not a direct reading of your metabolism.
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Why do different calculators produce similar numbers?
Calculators that use the same or similar MET value, body-mass input, duration, and conversion can arrive at similar estimates. The Compendium of Physical Activities provides reference MET values so researchers can assign activity energy costs consistently and compare results across studies. Its values are also used in public-health research and consumer health technologies.
That shared framework does not show that every website uses the same formula implementation, activity selection, or output definition. A calculator might choose a different value for an activity or handle the energy total differently, even if its result looks similar.
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Where do the activity values come from?
The 2024 Adult Compendium update reports values for 1,114 activities under 22 major headings: 912 values were measured and 202 were estimated. Its stated target population is adults aged 19–59. The update added activities and revised existing values using evidence published since the prior update.
Do these 3 things before closing this tab:
1Clear out junk files and repair common Windows errors2Scan for outdated or missing drivers - takes under a minute3Repair Windows errors before they cause bigger problemsThese figures describe that Compendium release; they do not establish that every consumer calculator uses it. The Compendium is a reference for assigning activity-level energy costs, not a personalized measurement for each person.
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Why the number is not exact for you
A standard MET is a convention based on a resting oxygen-use rate of 3.5 mL/kg/min. An earlier Compendium paper cautions that individuals’ energy expenditure for the same activity can differ substantially from the stated mean MET value. A generic activity category cannot account for every person’s physiology or every difference in how an activity was performed.
So treat a calculator result as an approximation. It can be useful as a consistent estimate, but it does not prove that you burned exactly the displayed number of calories.
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What to check when comparing calculators
- Activity value: Which activity and MET value does the calculator select?
- Inputs: Does it use body mass and activity duration?
- Meaning of the output: Is it estimating energy for the activity alone, or reporting a broader daily total?
- Basis: Does it use standardized reference values or individualized measurements?
The sources establish a common MET-based framework, but they do not establish how every current calculator handles these choices. Similar-looking totals alone cannot tell you which assumptions a particular tool uses.
About the copy button
I noticed the issue while trying to copy a calculator result: the button appeared to give me a different value from the one shown. Without the specific calculator, copied output, and steps to reproduce it, I can’t establish what caused that discrepancy or whether the button was actually at fault. That reported experience is separate from the MET formula, which explains how estimates can be calculated but cannot verify a particular interface bug.
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