BODY FAT % · JACKSON-POLLOCK 7-SITE
SIRI EQUATION · CALIPERS REQUIRED
7-Site Skinfold Body Fat Calculator
Enter seven caliper measurements and your age to get a body fat % estimate using the full Jackson-Pollock 7-site equations - the most precise at-home skinfold protocol.
Reviewed by João Freitas
· Formula: Jackson-Pollock 7-site (Siri)
Where to pinch: the 7 sites
/measure-guide
All seven sites are pinched on the right side of the body (the standard convention), lifting skin + fat away from the muscle before placing the caliper jaws about 1 cm from your fingers. The same sites apply to men and women.
7-site landmarks
- Chest - diagonal fold halfway between the nipple and the armpit crease.
- Midaxillary - vertical fold on the mid-armpit line, level with the bottom of the sternum.
- Triceps - vertical fold at the back of the upper arm, halfway between shoulder and elbow.
- Subscapular - diagonal fold just below the bottom tip of the shoulder blade.
- Abdomen - vertical fold about 2 cm to the right of the navel.
- Suprailiac - diagonal fold just above the hip bone, following the natural line of the iliac crest.
- Thigh - vertical fold on the front midline, halfway between the hip crease and the top of the kneecap.
3-site or 7-site - which one?
/methods
Both use the same caliper technique and the same Siri equation - the difference is how many folds get averaged into the estimate. More sites means more chances for your technique to even out, at the cost of a longer measuring session.
When 7-site earns its keep
- You already own a caliper and check in monthly - the extra few minutes buys a steadier trend line.
- Your fat distribution isn't "typical" (noticeably more on the torso than the limbs, or vice versa) - extra sites reduce that bias.
- You want a number closer to what research studies validated against DEXA/BodPod, which mostly used the 7-site protocol.
When 3-site is enough
- You're new to calipers and just want a fast, repeatable trend - fewer sites, fewer chances to mis-measure.
- You're measuring solo and some sites (subscapular, midaxillary) are awkward to reach consistently on yourself.
- Try the faster 3-site calculator instead.
Body fat percentage categories (men & women)
General reference ranges from the American Council on Exercise (ACE). Healthy ranges shift with age, sport and genetics - use them as a guide, not a verdict.
| Category | Men | Women |
|---|
| Essential fat | 2-5% | 10-13% |
| Athletes | 6-13% | 14-20% |
| Fitness | 14-17% | 21-24% |
| Acceptable / average | 18-24% | 25-31% |
| Obesity | 25%+ | 32%+ |
FAQ
Do I need special calipers for the 7-site method?
A standard spring-loaded skinfold caliper works fine - you don't need a research-grade device. Just use the same caliper and technique every time so your trend stays reliable.
Why does 7-site use more sites than 3-site?
Adding midaxillary, subscapular and suprailiac gives four extra data points around the torso, which averages out a bad single measurement and works better if your fat distribution doesn't match the pattern the 3-site formula assumes.
Is 7-site more accurate than 3-site?
For most people it's a bit more accurate and more forgiving of an occasional bad pinch, since the error averages across seven readings instead of three. The trade-off is it takes longer and needs more sites you can reach consistently on your own.
Can I calculate body fat without entering my weight?
Yes - weight is optional. Without it you still get your body fat percentage and category. Add your weight if you also want the fat mass and lean mass breakdown in kilograms.
Related tools
References
- Jackson AS, Pollock ML. Generalized equations for predicting body density of men. Br J Nutr. 1978;40(3):497-504. doi:10.1079/BJN19780152
- Jackson AS, Pollock ML, Ward A. Generalized equations for predicting body density of women. Med Sci Sports Exerc. 1980;12(3):175-181.
- Siri WE. Body composition from fluid spaces and density. 1961. (Siri % body-fat equation.)
Disclaimer: educational purposes only. Not medical advice. If you have a medical condition, talk to a qualified professional.