Formula Hub

The Widmark formula estimates Blood Alcohol Concentration by dividing the total grams of alcohol consumed by body weight adjusted for a gender-based body-water distribution constant, then subtracting the amount the body has already metabolized over elapsed time at an average elimination rate. It is widely used to give a rough estimate of impairment level, though it is not a substitute for an actual breathalyzer or blood test.

Body Mass Index (BMI) is a simple, widely used metric to estimate whether a person has a healthy body weight relative to their height. BMI categorizes individuals into underweight (under 18.5), normal weight (18.5 - 24.9), overweight (25 - 29.9), and obese (30 and above). It acts as a screening tool to identify possible weight problems for adults.

Basal Metabolic Rate (BMR) represents the minimum number of calories your body needs to function at rest (e.g. breathing, circulation, cell production, temperature regulation). BMR is estimated using the Mifflin-St Jeor equation, which is widely considered the most accurate standard for calorie planning.

The U.S. Navy Method estimates body fat percentage from simple circumference measurements rather than calipers or DEXA scans, using a regression formula developed by Hodgdon & Beckett that predicts body density from waist, neck, hip (for women), and height, then converts that density to a body fat percentage using the Siri equation (the 495/D − 450 term).

The Mosteller formula is the simplest and most widely used method for estimating Body Surface Area, a measurement used clinically for drug dosing (especially chemotherapy) and for normalizing physiological measurements like kidney filtration rate (eGFR). Several other validated formulas exist (Du Bois, Haycock, Gehan & George, Boyd), each using slightly different regression coefficients, and are often averaged together since no single formula is universally agreed upon as most accurate.

This formula extends the Mifflin-St Jeor TDEE calculation one step further by applying a calorie surplus or deficit based on a specific weight goal, producing a single daily calorie target. It relies on the widely-used approximation that roughly 500 kcal of daily deficit or surplus corresponds to about 0.5 kg (1 lb) of body weight change per week.

There is no single, universally agreed-upon Ideal Body Weight (IBW) formula. Devine (1974), Robinson (1983), Miller (1983), and Hamwi (1964) are four separate, independently published clinical equations, each developed by different researchers using different population data, and each still in use today for different purposes (Devine, for example, is widely used in medical drug-dosage calculations). All four share the same basic structure — a base weight at 5 feet tall, plus a fixed amount added per inch of height above that — but use different constants, so they produce different results for the same person. Comparing all four together, rather than presenting one as definitive, gives a more complete and honest picture of what "ideal weight" estimates actually represent: a range, not a single number.

Lean Body Mass represents everything in the body except fat. The Boer formula estimates it directly from weight and height using gender-specific regression coefficients, without requiring a body fat percentage measurement. It is commonly averaged together with other validated equations (James, Hume formulas) for a more robust estimate, and is useful for tracking muscle mass and setting nutrition targets independent of fat mass changes.

Once a daily calorie target is set, that budget must be split across the three macronutrients. Each diet archetype allocates a different percentage of calories to protein, carbs, and fat — for example, a ketogenic diet allocates only 5% to carbs and 75% to fat, while a balanced diet spreads more evenly. Converting each macro's calorie share into grams requires dividing by its calories-per-gram value (4 for protein/carbs, 9 for fat, since fat is more energy-dense).

Pace and speed describe the same underlying relationship between time and distance, just inverted. Pace expresses how much time it takes to cover one unit of distance (useful for runners tracking minutes per km or mile), while speed expresses how much distance is covered per unit of time (more common for cycling or driving). Once a known pace is established from a training run or previous race, that same pace can be used to predict a finish time for a different target distance, assuming a similar effort level is maintained.