Insulin Sensitivity Factor (ISF / Rule of 1800) Calculator

Enter height and weight to get your BMI and category (underweight / normal / overweight / obese).

Estimate daily BMR and TDEE using Mifflin-St Jeor or Harris-Benedict, with calorie targets for cutting and bulking.

Estimate body fat percentage using the US Navy circumference formula (neck, waist, plus hip for women).

Suggest ideal bedtimes or wake times based on 90-minute sleep cycles, so you wake up between cycles instead of mid-deep-sleep.

Estimate daily water intake from body weight, exercise duration and climate so you stay hydrated without overdoing it.

Compute pace per km / per mile from distance and time, or project finish time from a target pace — covers 5K, 10K, half- and full-marathon distances.

Compute 5 training heart rate zones from age and optional resting HR using the Karvonen formula (Z1 warm-up to Z5 max effort).

Estimate lean body mass (LBM), fat mass and body fat % from height, weight and sex using the Boer, Hume and James formulas.

Split a daily calorie target into grams of carbs, protein and fat at any macro ratio.

Estimate one-rep max from a sub-maximal lift (weight × reps) with Epley, Brzycki, Lombardi and Lander formulas, plus a 50–95% intensity training table.

Estimate body surface area from height and weight using the Mosteller, Du Bois, Haycock and Boyd formulas — commonly used in drug-dosing, chemotherapy and cardiac-index calculations.

Project a finish time at one distance from a known time at another distance using the classic Riegel formula T₂ = T₁ × (D₂/D₁)^1.06.

Compute mean arterial pressure from systolic and diastolic blood pressure with clinical bands and pulse-pressure context: MAP = DBP + (SBP − DBP)/3.

Compute cumulative smoking exposure in pack-years from cigarettes per day and years smoked, with lung-cancer-screening thresholds.

Divide waist by hip circumference and check the WHO risk bands — a quick screen for central obesity and cardiovascular risk.

Use METs, body weight and duration to estimate calories burned for common activities (running, hiking, swimming, cycling and more).

Pick the dose (mg) and the time you drank it; the calculator uses the standard ~5-hour caffeine half-life to project how many milligrams remain hour-by-hour, including the level at bedtime.

Bergman’s BAI estimates body-fat percentage from hip circumference and height alone (BAI = hip ÷ height^1.5 − 18) — no scale required.

Enter age, sex, height and weight to compare all five activity levels side-by-side — instantly see the daily calories you need to maintain weight.

Estimate blood alcohol concentration (BAC %) with the Widmark formula from drinks consumed, body weight, sex and hours elapsed — and compare against the Hong Kong 0.05% drink-driving limit.

Enter your distance covered in a 12-minute run to estimate VO₂ max and read off the age/sex fitness category.

Enter your bodyweight and training goal to get a science-backed daily protein range (g/day) and per-meal split, based on RDA, ISSN and ACSM/AND/DC guidelines.

Enter your last menstrual period (LMP) date and average cycle length to estimate the next ovulation day, fertile window and next period.

Estimate total body water (in litres) and the percentage of body weight using the Watson formula based on age, sex, height and weight.

Enter step count, height (auto-derives stride length) and body weight to estimate distance walked (km / mi), stride length, calories burned and your daily activity tier.

Enter a food's glycemic index (GI) and grams of carbs per serving to compute glycemic load GL = GI × carbs ÷ 100 — a better predictor of real blood-sugar response than GI alone.

Convert HbA1c (%) to estimated average glucose (eAG) in both mg/dL and mmol/L — and back again — to help diabetes and prediabetes patients read their lab reports.

Enter height, weight and body-fat percentage to compute Fat-Free Mass Index (FFMI) and the height-adjusted FFMI used to gauge muscularity.

Enter height and sex to compare the four classic ideal-body-weight formulas (Devine, Robinson, Miller, Hamwi), with their average and a ±10 % healthy-weight band.

Select 0–2 points for each of the five APGAR signs (Appearance / Pulse / Grimace / Activity / Respiration) to get the total APGAR score (0–10) and clinical band (normal / moderately depressed / severely depressed).

Pick eye-opening (1–4), verbal (1–5) and motor (1–6) responses to compute the Glasgow Coma Scale total (3–15) with mild / moderate / severe banding.

Enter systolic (SBP) and diastolic (DBP) blood pressure; the tool returns the pulse pressure and mean arterial pressure (MAP), then classifies the result as low / normal / elevated using the < 40, 40–60 and > 60 mmHg bands — the textbook signal for cardiovascular risk on a routine BP report.

Enter serum creatinine, age and sex; the tool applies the 2021 NKF / ASN-recommended CKD-EPI formula (race-free) to estimate glomerular filtration rate (eGFR) and classifies the result into CKD stages G1–G5 — the standard reading of a kidney-function lab report.

Enter age, weight, serum creatinine and sex; the tool applies the 1976 Cockcroft–Gault formula to estimate creatinine clearance (CrCl, mL/min) — still the FDA- and EMA-required formula for renal dose adjustment in most drug labels.

Enter waist circumference and height in any units; the tool returns the waist-to-height ratio (WHtR) and classifies it against the universal "keep your waist to less than half your height" cut-off (< 0.5) — a more sensitive central-obesity signal than BMI.

Computes the pediatric maintenance IV fluid rate (mL/hr and mL/day) from body weight using the Holliday-Segar 4-2-1 rule — the standard since the original 1957 publication.

Enter total cholesterol, HDL and triglycerides; the Friedewald equation (LDL = TC − HDL − TG / 5 or / 2.2 SI) estimates LDL-C and grades the result by NCEP ATP III risk bands.

Enter your current weight, target weight and daily calorie deficit; the tool uses the "≈ 3 500 kcal per lb of body fat" rule of thumb to project the number of weeks and the expected date you will reach your goal — a sanity check for setting a sustainable pace.

Enter pre / post-exercise body weight, fluids consumed and session length; the tool returns sweat rate per hour (L/h) and a suggested fluid intake every 15 minutes per the ACSM hydration guidelines — used by runners, cyclists, footballers and recruits.

Enter a drink's volume (ml) and alcohol content (ABV %); the tool converts to standard drinks using each region's definition (US 14 g, UK 8 g, AU/HK 10 g, JP 20 g of pure alcohol) and compares with WHO and national low-risk guidelines (e.g. ≤ 10 drinks/week).

Enter height and waist circumference; the tool applies the Thomas (2013) Body Roundness Index BRI = 364.2 − 365.5·√(1 − ((WC/2π) ⁄ (0.5·h))²). BRI tracks visceral fat and metabolic-disease risk more closely than BMI — a JAMA 2024 study linked BRI to cardiovascular mortality.

Enter visual acuity in Snellen (20/20, 20/40, etc.), metric Snellen (6/6, 6/12), LogMAR or decimal; the tool returns the other three formats with reference thresholds for driving licences and the legal-blindness cut-off — the standard conversion for ophthalmology, optometry and driving / occupational medicals.

Tick the burned regions (head, anterior / posterior torso, arms, legs, perineum) and the patient age group (adult / child); the tool applies Wallace's Rule of Nines to return total body-surface-area burned (%TBSA) and shows the Parkland fluid-resuscitation target — the standard field tool in emergency medicine, fire-rescue and first-aid.

Enter body weight, sex and the powerlifting total (squat + bench + deadlift, in kg or lb); the tool applies the Wilks 2020 coefficients to return the Wilks score — the standard way to compare powerlifters across body-weight classes and sexes, and the basis of best-lifter awards in IPF, USAPL and many federations.

Enter total carbohydrates, dietary fibre and sugar alcohols (per serving); the tool returns Net Carbs = total carbs − fibre − ½ × sugar alcohols. The standard keto / low-carb / diabetic-diet metric for absorbable carbs per serving.

Enter heart rate (HR) and stroke volume (SV); the tool computes cardiac output Q = HR × SV (L/min) and, given body surface area (BSA), the cardiac index CI = Q / BSA. Core hemodynamic math for emergency medicine, cardiology and nursing.

Enter weight and body-fat percentage; the tool returns BMR via the Katch-McArdle formula (BMR = 370 + 21.6 × lean body mass in kg) and TDEE after an activity multiplier. More accurate than Mifflin-St Jeor for lean and athletic body types where fat mass varies widely.

Enter the child's weight (kg), prescribed dose (mg ⁄ kg ⁄ dose or mg ⁄ kg ⁄ day), dosing frequency and adult-equivalent maximum; the tool returns the per-dose and total-daily amounts and flags when the adult cap is exceeded. The bread-and-butter weight-based dosing framework used in paediatrics worldwide.

Enter wet-bulb, globe and dry-bulb temperatures; the tool returns WBGT via the ISO 7243 formula 0.7·Tnwb + 0.2·Tg + 0.1·Tdb and classifies the result against the NIOSH / US military flag system (white / green / yellow / red / black) — the international standard for assessing heat-stroke risk in sport and occupational settings.

Enter cadence (steps per minute) and stride length (cm or m); the tool returns running speed (km/h, mph), pace (min/km, min/mi) and distance per minute — handy for runners on Garmin, Apple Watch and Strava tuning cadence vs stride.

Enter height and wrist circumference; the tool applies Grant's index r = height ÷ wrist circumference to classify body frame (small / medium / large) — used to adjust "ideal weight" estimates and reflects bone-structure differences that a single BMI value cannot.

Enter inseam (the floor-to-crotch length); the tool returns the recommended saddle height using LeMond's formula (inseam × 0.883, bottom-bracket to top-of-saddle) and the Hamley/Holmes method (~109% inseam to pedal), together with the 25°–35° knee-angle range for reference.

Enter treadmill speed (km/h or mph) and incline (%); the tool uses the ACSM running metabolic equation to return the equivalent flat-ground pace (min/km and min/mile) so you can compare indoor and outdoor effort.

Pick a fasting protocol (14/10, 16/8, 18/6, 20/4, OMAD, etc.) and your last-meal time; the tool returns when you can break the fast next, tomorrow's eating-window start and end, and total weekly fasting hours — useful for planning an IF schedule.

Enter your target hours per night plus the actual hours slept each of the past 7 nights; the tool returns total accumulated sleep debt (hours), average nightly shortfall, and how many consecutive "+1 h" nights are needed to clear it.

Enter your age; the tool reports the recommended sleep range from the US National Sleep Foundation's 2015 consensus guidelines (newborns 14–17 h, infants 12–15 h, preschoolers 10–13 h, adults 7–9 h, older adults 7–8 h) and a suggested bed-and-wake schedule.

Enter your height and a target BMI (e.g. 22.0); the tool computes the matching weight from W = BMI × (height/100)² in both kg and lb, plus how much you need to gain or lose from your current weight.

Enter the carbohydrate grams in a meal, pre- and post-meal glucose, the rapid-acting insulin units used and the glucose target; the tool applies the 500/TDD rule with the insulin sensitivity factor (ISF) to give a personalised ICR (g of carb per 1 U of insulin) and a suggested bolus.

Enter the total running time (hh:mm:ss) and distance (km or mile); the tool returns pace per kilometre, pace per mile, average speed (km/h, mph) and per-km / per-mile split tables — a quick way to compare training and race performance.

Enter your peak heart rate at end of exercise (HR_peak) and 1-minute post-exercise heart rate (HR_1min); the tool computes HRR = HR_peak − HR_1min — a cardiovascular fitness indicator from Cleveland Clinic (Cole et al., NEJM 1999): HRR ≤ 12 bpm is high-risk, 18–24 is average, ≥ 25 is good / athletic.

Enter your FTP (Functional Threshold Power, watts); the tool applies the Coggan 7-zone model to give the upper and lower bounds (Z1 Active Recovery → Z7 Neuromuscular Power) for every training zone — works for indoor trainers, road riding and Zwift sessions alike.

Enter the control-event rate (CER) and the experimental-event rate (EER); the tool returns the absolute risk reduction ARR = CER − EER, the relative risk reduction RRR and the number needed to treat NNT = 1 / ARR — the cornerstone metrics for reading clinical trials and evidence-based medicine.

Enter events and non-events in the exposed and control arms (the classic 2×2 table); the tool returns the risk ratio (RR), odds ratio (OR), risk difference (RD) and their 95 % confidence intervals — the core statistics for cohort and case-control epidemiology.

Enter the patient weight in kg; the tool applies the Holliday-Segar 4-2-1 rule to compute the maintenance IV fluid rate (mL/hr) and total daily volume (mL/day) — the standard bedside estimate for paediatric and adult inpatient fluid orders, useful for clinicians, nurses and pharmacists.

Enter the measured QT interval (ms) and heart rate (bpm) (or RR interval); the tool reports QTc using all four standard corrections — Bazett, Fridericia, Framingham and Hodges — and flags values outside the normal range. Essential for ECG interpretation and monitoring of QT-prolonging drugs.

Enter total volume, infusion time and the tubing drop factor (gtt/mL; macro 10/15/20, micro 60); the tool returns the required drops per minute (gtts/min) and the equivalent mL/hr — the standard bedside calculation for nurses, ER and IV-therapy clinicians.

Enter serum Na⁺, Cl⁻ and HCO₃⁻ (optionally K⁺ and albumin); the tool reports the anion gap AG = Na − (Cl + HCO₃), the albumin-corrected gap and a classification of metabolic acidosis (high vs. normal gap) — a staple for emergency, ICU and nephrology interpretation of blood-gas and electrolyte panels.