How We Calculate

How the AthleteCalcs tools work, where the formulas come from and what the results can and cannot tell you.

Our approach

A calculator is only useful if you can see how it reached its answer. Each AthleteCalcs page explains its method in plain language, names the formulas and published figures behind it and tells you which numbers are defaults you should replace. We use published formulas and public sources, we avoid hidden assumptions and we do not let advertising change a result.

Strength

The one-rep max tools estimate your best single lift from a lighter set using published prediction formulas: Epley (1985), Brzycki (1993), Lombardi (1989) and O’Conner and colleagues (1989). Each formula adjusts your weight by a number that depends on the repetitions you completed, and the pages show them side by side because they differ most at higher repetitions. Strength standards use commonly cited bodyweight multiples for the bench press, squat and deadlift. Volume load is sets × repetitions × weight, a standard training-load measure.

Running

Pace tools use plain arithmetic: pace is time divided by distance, and a speed in miles per hour converts to minutes per mile by dividing 60 by the speed. Race distances use their official lengths, and miles and kilometers convert at 1 mile = 1.60934 kilometers. The race time predictor estimates a finish time at one distance from a result at another, which only holds if you have trained for the longer distance.

Cardio and endurance

Heart rate zones use the Karvonen heart rate reserve method, which applies a percentage to the difference between your maximum and resting heart rate. When you do not know your maximum, the pages estimate it as 220 minus your age, a population average that can differ noticeably from your real maximum. Stride-based tools estimate walking stride length as roughly height × 0.413, with running stride longer because of the extra leg extension and airtime.

Military fitness tests

The military tools follow the structure of each test, for example the Air Force test’s push-ups, sit-ups, 1.5-mile run and waist measurement, and the Marine Corps test’s pull-ups or push-ups, plank and 3-mile run. The scoring bands on the pages are simplified approximations for planning and practice. They are not the official regulation tables, which change and differ by age and sex, so check your branch’s current standards.

Body and nutrition

Resting energy use is estimated with the Mifflin equation (1990), and the calorie tools use the common approximation of about 3,500 kilocalories per pound of body fat. That figure is a rule of thumb: real weight change varies with individual metabolism and shifts over time. Waist-to-hip ratio categories come from World Health Organization thresholds, unit conversions use exact factors such as 1 inch = 2.54 centimeters and the macro tools apply the usual structures, such as the very low carbohydrate, moderate protein, high fat pattern of a ketogenic diet.

Quizzes

The five quizzes ask a few questions and apply fixed rules to match you to a result, such as a body type, a running plan or a workout split. They are not scored by a model and the result is a suggestion, not a prescription. Your answers travel in the result page’s address, which the privacy policy explains.

Limits

A formula turns a few inputs into one number, and a person is more than a few inputs. Estimates are most useful for planning and for comparing options, and least useful as a precise target. If a result matters for your health or safety, check it with a qualified coach, trainer or doctor.