Body · Energy · Strength · Cardio · Recovery
Calculate it. Then do it.
Free health & fitness calculators, guided at-home sessions, and gear we’ve actually tested. No signup, no fluff.
The Index · Every instrument
The whole toolkit
Forty-five free calculators, by department. Run-counts are this month’s. Jump to a category, or filter with search above.
Body & CompositionMeasure where you stand
9 tools- 01BMIBody mass index, with healthy-range band980k
- 02Body Fat %U.S. Navy tape method estimate301k
- 03BMRResting energy, Mifflin–St Jeor274k
- 04Ideal WeightFour classic formulas, side by side188k
- 05Lean Body MassFat-free mass from weight & BF%122k
- 06Waist-to-Hip RatioA simple cardiometabolic risk proxy96k
- 07Body Surface AreaDu Bois & Mosteller, m²61k
- 08Frame SizeWrist-based small / medium / large48k
- 09Army Body Fat %NewU.S. Army circumference method (AR 600-9)New
Energy & NutritionFuel the work
9 tools- 10TDEE / CaloriesDaily burn — our most-used tool1.1M
- 11Macro SplitterProtein / carb / fat grams by goal612k
- 12Protein IntakeGrams per day from bodyweight340k
- 13Water IntakeDaily fluid target by weight & sweat219k
- 14Calorie DeficitLoss rate from a chosen deficit203k
- 15Maintenance CaloriesHold-steady intake at your activity158k
- 16Meal CaloriesSplit a daily target across meals74k
- 17Carb CyclingHigh / low day carbs around training52k
- 18Fiber TargetNewDaily fiber from energy intakeNew
Strength & TrainingMove heavier, smarter
9 tools- 19One-Rep MaxEpley & Brzycki, with % chart388k
- 20Wilks / DOTS ScoreCompare lifts across bodyweights141k
- 21Plate LoaderWhat to put on each side of the bar133k
- 22Training VolumeSets × reps × load, per muscle98k
- 23Powerlifting TotalSquat + bench + deadlift, ranked87k
- 24Strength StandardsNovice → elite by lift & weight76k
- 25RPE ConverterRPE ↔ % of 1RM, reps in reserve58k
- 26Warm-up SetsRamp-up scheme to your top set41k
- 27Rest Timer CalcNewRest by goal: strength vs hypertrophyNew
Cardio & EnduranceGo further, faster
9 tools- 28Pace CalculatorTime, distance & pace, any unit204k
- 29VO₂ MaxEstimate from a field or race test167k
- 30Heart-Rate ZonesFive zones from max or reserve155k
- 31Race Time PredictorRiegel projection across distances112k
- 32Running CaloriesBurn by pace, weight & distance99k
- 33Treadmill PaceSpeed ↔ pace, with incline offset68k
- 34Marathon SplitsEven or negative-split pace bands57k
- 35Cycling PowerWatts, W/kg & FTP estimate44k
- 36Calories BurnedNewEnergy used by any activity & MET valueNew
Recovery & WellnessAdapt, don’t just grind
9 tools- 37Sleep CycleBest bed / wake times by 90-min cycles186k
- 38Sleep DebtAccumulated shortfall vs your need142k
- 39Max Heart RateTanaka & 220-age, compared131k
- 40HydrationFluid & electrolyte loss replacement88k
- 41Steps → CaloriesEnergy burned from a step count79k
- 42Daily Step GoalTarget steps for your activity goal66k
- 43Caffeine TimingCut-off for a clean night’s sleep54k
- 44Recovery ScoreNewReadiness from sleep, soreness & HRVNew
- 45Nap TimerNewIdeal nap length to wake without grogginessNew
Workouts & Recovery · Guided sessions
Then do it
Free, follow-along sessions that coach you move by move — name the move, cue the form, time it, and tell you what's next. No account, no streak, works offline. Start with the moment you're in.
- Stressed or wiredBreatheBox breathing, 4-7-8, coherent breathing — each inhale and exhale paced for you.Start
- Got 10 minutesQuick workoutA no-equipment bodyweight circuit, coached move by move with timed work and rest.Start
- Stiff from sittingLoosen upA guided stretch and mobility flow that undoes screen slump in a few minutes.Start
- Can't switch offWind downA long-exhale 4-7-8 session to slow the breath and settle before sleep.Start
RankingsRanked from the test bench — re-scored each quarter
16 rankedBest smartwatches, tested on-wrist · 16 watches logged for GPS accuracy, heart-rate tracking and real-world battery.
- Apple Watch Ultra 2Best overall
The most accurate heart-rate and GPS in test, a two-day battery and the deepest health suite on the wrist.
9.3/ 10 - Garmin Fenix 8Best for training
Multi-week battery, the richest training-load and recovery metrics, and maps that work off-grid.
9.1/ 10 - Samsung Galaxy Watch 7Best for Android
Sharp AMOLED, solid sleep and BIA body metrics — the pick if you carry a Galaxy phone.
8.8/ 10 - Apple Watch Series 10Best for iPhone
Thinner case, bigger always-on display and the full Apple health suite for most people.
8.7/ 10 - Apple Watch SE (3rd gen)Best value
Nearly all the everyday tracking of the flagship for far less; you lose the always-on screen and ECG.
8.6/ 10
ComparisonsHead-to-head, spec for spec
6 matchupsThis week: Oura Ring 4 vs Ultrahuman Ring Air — price, specs and our verdict, side by side.
Ultrahuman Ring Air
Oura-class sleep data with no membership; the app is busier and metabolic features are still maturing.
Oura Ring 4
Best-in-test sleep staging and HRV, the most polished app — held back only by the monthly fee.
| Spec | WinnerOura Ring 4 | Ultrahuman Ring Air |
|---|---|---|
| Price | $349 | $349 |
| Battery life | ~7 days | ~6 days |
| Form | Titanium ring | Titanium ring |
| Sleep tracking | Best-in-test staging | Strong |
| Subscription | Required ($5.99/mo) | None |
| Water resistance | 100m | 100m |
| FitHQ score | 9.0 / 10 | 8.6 / 10 |
Published formulas
Every tool cites the equation it uses — Mifflin, Riegel, Tanaka and more.
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