Example 1
- Lean mass: 58 kg
1623 kcal/day
58 kg FFM gives about 1623 kcal of Katch BMR.
Katch McArdle calculator
Type fat-free kilograms, or total mass and body-fat percent. Katch is 370 plus 21.6 times lean. Fifty-eight kg FFM is 1623 kcal. Mifflin from weight, height, and age lives on another page.
Katch = 370 + 21.6 × kg FFM. Mifflin is on the BMR calculator. Girth BF% is on the US Navy method.
Result
Lean mass (kg), Body fat % (optional), Total mass (when using BF%) and Activity (PAL, for Katch TDEE). Katch-McArdle BMR shows up here.
How it works
Katch-McArdle is simple once you already have fat-free mass: 370 plus 21.6 times kilograms of FFM. Fifty-eight kg is 1623 kcal, because 21.6 × 58 is 1252.8, and adding 370 leaves 1622.8, rounded up. Fifty kg FFM lands on a clean 1450. Sixty-five kg FFM is 1774. Forty-five kg FFM is 1342. Height, age, and sex do not enter that constant.
If you only know scale weight and a body-fat percent, the calculator builds lean first: mass times (1 minus BF/100). Eighty kilograms at 20% is 64 kg lean and about 1752 kcal. Seventy kilograms at 15% is 59.5 kg and about 1655 kcal. Ninety kilograms at 25% is 67.5 kg and 1828 kcal. Seventy-five kilograms at 18% is 61.5 kg and about 1698 kcal.
People search BMR and land on Mifflin, because that page is the familiar one. Mifflin on CalcBoxer takes mass, height, age, and sex, with no body-fat percent. Here the percent is an input, or you type FFM from DEXA, a scale, or Navy. Two paths, one Katch formula. One complete path is enough.
Activity is optional. PAL multiplies Katch BMR and shows TDEE from the same 370 plus 21.6 constant. The TDEE page multiplies Mifflin. The same 1.55 factor can therefore make two different days. The Mifflin comparison block (age, sex, height, and an optional other mass) is there so you can see a difference beside Katch, not so it replaces the BMR card.
The US switch converts pounds and inches with 0.453592 and 2.54. Pounds apply to lean or total mass. Inches apply only to height in the comparison. FFMI takes the same FFM and divides by meters squared. There are no kilocalories there. There is no height in the main formula here. WHR and waist do not enter either.
Type 58 in the lean-mass field and click Calculate, or leave that field and give 80 kg plus 20%. Both routes return Katch, not a meal plan. Treat 1623 kcal as a lean-mass sketch for class, not as a deficit prescription.
How to use
- If you already know FFM from DEXA, a scale, or Navy, type fat-free mass in kilograms or pounds.
- Or leave that field and type total mass plus body-fat percent. Then lean = mass × (1 minus BF/100).
- Click Calculate. 58 kg FFM is 1623 kcal per day. PAL, if you pick it, multiplies that same Katch number.
- Fill age, sex, and height only when you want Mifflin beside it, for a difference, not instead of Katch.
- The calculator does not guess body-fat percent from the waist. Navy and WHR live on their own pages.
Formula
BMR = 370 + 21.6 × kgFFM
Lean from mass and BF%: kg × (1 - BF/100). Not Mifflin.
Katch BMR from lean mass
BMR is 370 plus 21.6 times fat-free kilograms. 58 kg FFM is 1623 kcal. Mifflin from weight, height, and age is only an optional second line.
- BMR
- Basal Metabolic Rate via Katch-McArdle: 370 + 21.6 × kg FFM. At 58 kg lean that is 1623 kcal, with no age or height in that row.
- FFM
- Fat-free mass. Type it directly or build it from mass and BF%: kg × (1 − BF/100). That lean mass is what 370 + 21.6× uses.
- Katch
- Katch-McArdle on this page, not Mifflin. Mifflin wants weight, height, and age; Katch wants lean, which is why 58 kg FFM is 1623.
- PAL
- An activity factor for optional Katch TDEE. Sedentary ×1.2 on a 1623 BMR would be about 1948; skip PAL and you keep BMR alone.
- Mifflin
- An optional second sketch after age, sex, height, and a Mifflin mass. The headline 1623 still comes from Katch and FFM.
Examples
Example 2
- Mass: 80 kg
- BF%: 20
1752 kcal/day
80 kg and 20% BF is 64 kg FFM, which gives about 1752 kcal.
Example 3
- Lean mass: 50 kg
1450 kcal/day
50 kg FFM gives exactly 1450 kcal.
Example 4
- Mass: 70 kg
- BF%: 15
1655 kcal/day
70 kg and 15% BF gives about 1655 kcal.
Example 5
- Lean mass: 65 kg
1774 kcal/day
65 kg FFM gives 1774 kcal.
Example 6
- Mass: 90 kg
- BF%: 25
1828 kcal/day
90 kg and 25% BF gives 1828 kcal.
Example 7
- Lean mass: 45 kg
1342 kcal/day
45 kg FFM gives 1342 kcal.
Example 8
- Mass: 75 kg
- BF%: 18
1698 kcal/day
75 kg and 18% BF gives about 1698 kcal.
Frequently asked questions
Why is 58 kg FFM 1623 kcal, not 370?
Because 21.6 times 58 is 1252.8. You add 370. 1622.8 rounds to 1623 kcal per day.
How is Katch different from Mifflin on the BMR page?
Katch is 370 plus 21.6 times lean kilograms. Mifflin is 10m plus 6.25h minus 5a, then plus 5 or minus 161. Different inputs, different result.
How do I use weight and percent instead of FFM?
Type total mass and BF%, and leave the lean field. 80 kg and 20% is 64 kg FFM and about 1752 kcal.
Where do I get body-fat percent?
Navy, DEXA, or a scale with BF. Here % is an input. WHR and BMI do not compute that percent.
Is TDEE from PAL here the same as Mifflin times PAL?
No. PAL multiplies Katch BMR. The TDEE page multiplies Mifflin. The same 1.55 can make two different days.
Why is there a Mifflin comparison block?
So you can see a difference on the same data. Katch stays the main result. Full Mifflin lives on the BMR page.
Does FFMI use the same 370 plus 21.6?
No. FFMI is FFM over height squared. There are no kilocalories there. There is no height in the main formula here.
What do I get at 50 kg FFM?
A clean 1450 kcal. 65 kg FFM is 1774, and 45 kg FFM is 1342.
What do I get at 70 kg and 15% BF?
Lean 59.5 kg and about 1655 kcal. 75 kg and 18% is about 1698, and 90 kg and 25% is 1828.
Is the 20% at 80 kg guessed from the waist?
No. You type 20% yourself. Waist and hip live on WHR. Navy has its own girth formula. This calculator does not read girths.
Knowledge sources
Resting calories here use Katch–McArdle from FFM, not Mifflin and not a lab measurement.
Page updated in 2026.