Health Tools
Quick health and fitness calculators, from BMI and body fat to daily calorie needs and ideal weight — handy estimates you can run in seconds.
Calculate your Body Mass Index in metric or imperial units and see the category — along with an honest account of what BMI does not measure.
Calorie CalculatorEstimate your daily calorie needs from age, sex, height, weight and activity using the Mifflin-St Jeor equation, with the error margins stated honestly.
Running Pace CalculatorCalculate running pace, time or distance — enter any two and get the third — with split tables for the standard race distances.
Macro CalculatorSplit your daily calories into protein, carbohydrate and fat based on your goal, with the calorie values per gram and the evidence behind protein targets.
One Rep Max CalculatorEstimate your one-rep max from the weight and reps of a set, using several established formulas, with the rep range where the estimate is actually reliable.
Water Intake CalculatorEstimate how much water to drink each day from your weight and activity — with a straight answer about where the eight-glasses rule came from.
Ideal Weight CalculatorEstimate ideal body weight from height and sex using the classic clinical formulas, with a frank explanation of where those formulas came from.
Body Fat CalculatorEstimate body fat percentage using the US Navy circumference method, with the accuracy range and how it compares to more direct measurements.
Color Blindness TestA colour vision screening covering red-green, blue-yellow and total colour blindness — an indication only, not a diagnosis.
Nutrient-Rich Food FinderPick a nutrient — iron, fibre, potassium, B12 and eleven more — and see the best food sources ranked, with what affects absorption.
Food Calorie & Nutrition LookupCalories, protein, carbohydrate and fat for common foods, searchable with portion scaling — and what the numbers do not capture.
Calories Burned by ActivityCalories burned across 32 activities from official MET values, calculated from your weight and duration — with why the number is an estimate, not a measurement.
Health Reference RangesStandard guideline ranges for blood pressure, heart rate, BMI, sleep, A1C, glucose and cholesterol, gathered in one place with their sources noted.
Clinical Score CalculatorMean arterial pressure is not the average of systolic and diastolic — the shortcut overstates it by exactly the pulse pressure over six.
Creatinine Clearance & eGFR ComparisonCockcroft-Gault is linear in body weight and CKD-EPI ignores weight entirely — so which reads higher is decided by the patient size.
Burn TBSA & Parkland CalculatorBoth the adult and paediatric charts total 100, because the head and leg differences cancel — which is exactly why using the wrong one hides.
Lab Value CalculatorA low albumin hides a raised anion gap — 34% of apparently-normal gaps correct to raised, and none ever correct back.
Paediatric Fluid & Dose CalculatorThe 4-2-1 rule and Holliday-Segar are taught as the same rule in different units. They are not — they cross at exactly 35 kg.
Vital Signs by AgeAn infant entire normal heart rate range sits outside the adult one — and breathing rate stays misleading twice as long as pulse.
IV Drip Rate CalculatorOn a 60 gtt/mL set, drops per minute equals mL per hour exactly — which is the whole reason microdrip sets are 60.
Oxygen Tank Duration CalculatorThe same gauge reading means 19 minutes or six hours depending only on which cylinder — and the gauge overstates the time left.
ABG Interpretation TrainerCompensation essentially never normalises the pH — so a normal pH with abnormal chemistry is a mixed disorder, not a compensated one.
About these health tools
Body mass index is the most quoted number in this category and the one most worth understanding the limits of. It divides weight by the square of height — but people are three-dimensional, and mass scales closer to the cube of height than the square. The consequence is systematic rather than random: BMI runs high for tall people and low for short people of identical build. Adolphe Quetelet, who devised it in the 1830s, was describing populations rather than assessing individuals, and said so at the time. It also cannot distinguish muscle from fat, which is why well-trained athletes routinely land in the overweight band. None of that makes it useless — it is cheap, reproducible and correlates well across large groups — but it is a screening flag rather than a diagnosis. A second thing worth knowing is what a laboratory reference range actually is. It is usually the middle 95 per cent of a reference population, which means that by construction one healthy person in twenty falls outside it on any given test. Run twenty tests on a perfectly healthy person and the odds are better than even that at least one comes back flagged. That is arithmetic rather than illness, and it is why a single out-of-range value on a broad panel is usually a reason to repeat the test rather than to worry. The third is that most health calculators estimate a population average and present it as a personal figure. Calorie equations carry a standard error of several hundred calories a day between individuals of identical height, weight, age and sex — the formula says where the middle of the distribution sits, not where you sit in it. Measured results over a few weeks beat any equation, which is the honest use for these tools: a starting point to adjust from rather than a target to obey.