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Health & Body

Free health calculators: BMI, body fat, BMR, lean body mass, ideal weight, waist ratios, A1C, water intake and sleep — imperial and metric units with clear, informational explanations.

13 calculators Free and online

📌 About Health & Body

Body metrics like BMI, body fat percentage and your basal metabolic rate give a quick, standardized snapshot of where you stand, and they're a useful starting point for a conversation about your health. These calculators use the established formulas — Mifflin-St Jeor for resting calories, the U.S. Navy tape method for body fat, Boer for lean mass — and show each result alongside what the number actually means.

Results are for general information only and are not medical advice. Estimates from population formulas can differ from a clinical measurement, so for personal guidance always talk to a qualified healthcare professional.

  • Calculate BMI, body fat and lean body mass in pounds and feet/inches or metric
  • See your BMR — the calories you burn at complete rest — with the Mifflin-St Jeor formula
  • Find your healthy weight range and check waist-to-height and waist-to-hip ratios
  • Translate an A1C result into estimated average glucose (eAG)
  • Estimate daily water intake and plan bedtimes around full sleep cycles
  • Understand what each number does and doesn't tell you

🧮 Calculators in this category

Body Composition

BMI Calculator — Body Mass Index in Pounds, Feet & Inches
Find your Body Mass Index from your height and weight, see your CDC weight category, and the healthy weight range for your height.
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Body Fat Calculator — U.S. Navy Method (Body Fat Percentage)
Estimate your body fat percentage from a few tape measurements using the U.S. Navy method — plus your category, fat mass and lean mass.
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Body Roundness Index Calculator — BRI from Waist & Height
Estimate your Body Roundness Index (BRI) from your waist circumference and height in inches — a newer shape-based marker that tracks visceral fat better than BMI.
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Lean Body Mass Calculator — Boer Formula (LBM & Body Fat Mass)
Estimate your lean body mass (everything that isn't fat) and your body fat mass in pounds, using the trusted Boer formula.
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Waist-to-Height Ratio Calculator — WHtR Health Risk Estimate
Divide your waist by your height to get your WHtR — a quick central-fat screen that often flags health risk better than BMI.
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Metabolism & Energy

BMR Calculator — Basal Metabolic Rate (Mifflin-St Jeor)
Estimate your Basal Metabolic Rate — the calories your body burns at complete rest — from your sex, age, height and weight, plus daily calorie needs at each activity level.
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Medication Costs

GLP-1 Cost Calculator — Ozempic, Wegovy, Mounjaro & Zepbound Out-of-Pocket
Estimate what a GLP-1 drug really costs you per month and over a full course — comparing cash list price, your insurance copay, and a manufacturer savings card.
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Sleep & Rest

Sleep Calculator — Best Bedtimes & Wake Times by Sleep Cycle
Find the best bedtimes or wake-up times based on 90-minute sleep cycles, so you wake up between cycles instead of mid-sleep.
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Blood Sugar

A1C Calculator — Convert A1C to Average Blood Sugar (eAG)
Convert A1C (%) to estimated average glucose (eAG) in mg/dL — or turn an average glucose back into an A1C — with the normal, prediabetes and diabetes ranges.
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Alcohol & Wellness

Blood Alcohol (BAC) Calculator — Widmark Estimate by Drinks & Weight
Estimate your blood alcohol content (BAC) from the number of standard drinks, your body weight, your sex and the hours since your first drink.
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Weight & Body

Ideal Weight Calculator — Devine, Robinson, Miller & Hamwi (lbs)
Find a sensible target weight in pounds from your sex and height using the Devine, Robinson, Miller and Hamwi formulas, plus the healthy BMI range.
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Body Measurements

Waist-to-Hip Ratio Calculator — WHR & WHO Risk Category
Divide your waist measurement by your hip measurement to get your WHR and see the WHO low/moderate/high risk band for your sex.
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Nutrition & Hydration

Water Intake Calculator — Daily Water Needs in Ounces, Cups & Liters
Estimate how much water to drink each day from your weight, workout time and climate — shown in ounces, 8-oz cups and liters.
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📝 Related articles

Read more about this topic on our blog.

Body Fat Percentage: How to Measure It at Home
How to measure body fat percentage at home: the US Navy tape method vs calipers, DEXA, and BMI, healthy ranges for men and women, and a step-by-step worked example.
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Understanding BMI: What the Number Actually Means
BMI is a quick screening number, not a diagnosis. Here's how the formula works, what the CDC categories mean, what BMI misses, and when the number actually matters.
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How Much Water Should You Drink a Day?
The 8x8 rule is a myth. Here's how much water you actually need based on body weight, exercise, climate, and pregnancy, plus the real signs of dehydration.
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How to Calculate Your TDEE (Total Daily Energy Expenditure)
Your TDEE is the total calories you burn in a day. Here's how to calculate it from your BMR and activity level, plus how to use it to lose fat or build muscle.
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❓ Frequently asked questions

How is BMI calculated?

In US units, BMI = 703 × weight (lb) ÷ height (in)². A BMI of 18.5–24.9 is considered normal weight by the CDC. BMI is a screening tool, not a diagnosis — it doesn't distinguish muscle from fat.

Which of these tools is most accurate for body composition?

No tape-and-formula method matches a DEXA scan, but body fat percentage (U.S. Navy method) and lean body mass (Boer) tell you more about composition than BMI alone, because they account for where you carry weight rather than just total pounds.

Are these health calculators a substitute for seeing a doctor?

No. They're informational estimates built on standard population formulas. Use them to understand the numbers and frame questions, but rely on a qualified healthcare professional for diagnosis or treatment.