Diet and body metrics in one calculator: Navy body fat from a tape measure, lean body mass, protein and macro targets, water intake, heart-rate zones, MET calorie burn, waist ratios, caffeine half-life, and a clearly-labeled rough BAC estimate — every formula shown with its work.
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FORMULA USEDDiet & Body Metrics Calculator
Body metrics with honest error bars
Every member of this family is a published formula applied to your inputs — which makes every result an estimate. Tape-measure body fat lands within roughly ±3–4 points of a DEXA scan for many adults and misses for others; MET burn rates and 220-minus-age heart rates are population averages with wide individual spread. Use them to set a baseline and track trends, not to make diagnoses.
The formulas inside
Navy body fat uses the circumference equations (men: height, waist, neck; women: height, waist, hip, neck). Lean mass comes either from your body-fat percentage or the Boer height–weight equation. Protein multiplies weight by 1.2–2.2 g/kg. Macros split calories at 4 kcal/g protein and carb, 9 kcal/g fat. Water starts at 30–35 ml per kg and adds exercise. Heart zones hang off 220 − age. BAC is the Widmark equation with r = 0.68 (male) / 0.55 (female) and a 0.015 g/dL-per-hour burn-off.
Picking a starting number
When in doubt, start with the body-composition members: body fat → lean mass → protein target → macro split. That chain gives every other member better inputs. Waist-to-height under 0.5 and a protein target in the 1.2–2.2 g/kg band are two of the most robust rules of thumb in this whole page — recalibrate every few weeks against real-world results, not against the calculator.
Worked example
Navy body fat for the male sample preset: height 178 cm, neck 38 cm, waist 85 cm.
The board shows ≈ 16.4% — fitness-to-average range, roughly.
At 70 kg and 20% body fat, that pairs with a lean mass of 56 kg and a 112 g protein target at 1.6 g/kg.
How to use it
Pick the metric or formula from the dropdown.
Fill the fields in centimeters and kilograms — a flexible tape, relaxed stomach, same time of day.
Read the result, the substituted formula, and the confidence note under the board.
Chain outputs forward: body fat → lean mass → protein → macros.
Share the link — it remembers the member and your numbers.
Frequently asked questions
How accurate is the Navy body fat method?
For many adults it lands within about ±3–4 percentage points of a DEXA scan, but it can miss badly for very muscular, very lean, or older bodies. Measure with the same tape at the same time of day and track the trend rather than trusting any single reading.
How much protein should I eat per day?
Evidence-based targets for active adults cluster around 1.2–2.2 g per kg of body weight: 1.2–1.6 for general health, 1.6–2.2 when building muscle or dieting. A 70 kg adult at 1.6 g/kg needs about 112 g per day. Healthy kidneys handle this range comfortably.
Can I use this BAC estimate to decide whether to drive?
No — never. The Widmark estimate swings widely with food, drink pacing, medication, and individual enzymes, and impairment begins well below any legal limit. The only safe reading after drinking is zero: if you have been drinking, do not drive, regardless of what this or any calculator says.
How much water should I drink daily?
A common planning formula is 30–35 ml per kg of body weight, plus extra for exercise (roughly 350 ml per half hour here). Food supplies about 20% of total fluid, and thirst remains the best regulator for healthy adults — treat the number as a floor for planning, not a quota.
What heart rate zone should I train in?
Most of a training week belongs in zones 2–3 (60–80% of maximum) for endurance and health, with zone 4–5 work added deliberately. But 220 − age has a standard deviation of 10–12 bpm versus tested maximums, so use perceived effort or a field test alongside the formula.
Why did my caffeine number drop so slowly?
Caffeine has an average half-life of about 5.5 hours, so half of a 200 mg dose is still circulating 5–6 hours later. Smoking clears it roughly twice as fast, hormonal contraceptives and pregnancy much more slowly — the member shows the average case, not yours.