What formula sits behind each tool, where its numbers come from, and what we do when one of them is wrong.
A pace or calorie tool is only worth bookmarking if the arithmetic underneath it is right. None of the math on ExerciseCalc is proprietary; every calculator applies a formula that has been published somewhere for decades. This page lists which one, names the source we check it against, says how often that gets revisited, and explains what happens when a reader catches a mistake.
The Pace Calculator, Marathon Pace Calculator, Treadmill Pace Calculator and the marathon pace chart all reduce to the same identity: pace equals time divided by distance. There is no model to argue with here, only arithmetic, so the only place error can creep in is unit conversion (miles to kilometers, or mph to minutes per mile), which is why every result on this site shows both units side by side. The Race Time Predictor is different: it projects a finish time at one distance from a result at another using Pete Riegel's exponential fatigue formula (T2 = T1 x (D2/D1)^1.06), first published in 1977 and still the standard reference method for race-time prediction in exercise-science literature. Riegel's exponent is a population average, not a personal law, so we describe the output as a prediction, not a guarantee, and say so on the page itself.
The Calories Burned and Running Calorie Calculator tools use the metabolic equivalent (MET) method: calories per minute equal the activity's MET value multiplied by body weight in kilograms and 3.5, divided by 200. MET values themselves come from the Compendium of Physical Activities, the peer-reviewed reference catalog originally compiled by Barbara Ainsworth and colleagues and published in Medicine & Science in Sports & Exercise, which assigns a MET value to running at a given pace, walking, cycling and hundreds of other activities. Because the Compendium reports intensity as a function of pace rather than a single flat number for "running," our calculators interpolate between the nearest published pace brackets rather than using one generic MET value for every speed. That is also why our guides describe calorie burn as a range tied to body weight and pace instead of a single fixed number per mile.
The Heart Rate Zone Calculator supports two methods, and the page tells you which one it is using. Entering only age uses the widely cited 220-minus-age estimate of maximum heart rate, split into standard percentage-of-max training zones. That formula is a population average with a wide individual spread, which we say plainly rather than presenting it as exact. Adding a resting heart rate switches the tool to the Karvonen method (Karvonen, Kentala and Mustala, 1957), which uses heart-rate reserve, the gap between resting and maximum heart rate, and generally tracks individual fitness more closely than the age-only formula.
The VO2 Max Calculator is built on the Cooper 12-minute run test, developed by Kenneth H. Cooper and published in 1968, which estimates VO2 max from the distance covered in twelve minutes of maximal effort. The conversion formula is VO2 max = (distance in meters minus 504.9) divided by 44.73. Field tests like this trade some precision for something a lab test cannot offer: you can run it yourself on a track with a stopwatch, and the calculator rates the result against standard age and sex normative tables so the number means something beyond a raw figure.
The Steps to Miles Calculator converts a step count to distance using stride length, either a value you enter directly or an estimate based on height, since stride length scales roughly with leg length and walking versus running gait changes it further. Because individual stride varies by several inches even at the same height, we tell users that entering a measured stride length, counted over a known distance, gives a materially more accurate result than the height-based estimate.
Every formula above was checked against its published source when the calculator was built, and gets rechecked whenever we update the tool or a reader flags something that does not match a hand calculation. The pace and unit-conversion math does not change, so those pages are stable by nature. The MET, Riegel, Karvonen and Cooper-test formulas are decades-old published methods that are not likely to be revised, but if a newer peer-reviewed update to the Compendium of Physical Activities or a comparable reference changes a value we cite, we update the affected calculator and note the change.
If a calculator returns a number that does not match your own hand calculation, or a guide states a pace, calorie or benchmark figure you can show is off, use the contact page and include the exact inputs you used. We re-run the math against the source formula, and if a page needs a fix, we make it and note the update rather than silently editing the page.
ExerciseCalc is free to use and is supported by display advertising and a small number of affiliate links; if you buy something after clicking one, we may earn a commission at no cost to you. That revenue has no bearing on which formula a calculator uses or what result it returns. Ads are labeled as ads, and the affiliate disclosure sits at the bottom of every page. As an Amazon Associate we earn from qualifying purchases.
Curious who actually writes and checks this material? See the authors page for who is behind everything published here.