How to measure sitting height
- Sit on a hard, flat chair or box with your back and the back of your head against a wall.
- Sit up straight, thighs level, looking straight ahead.
- Have someone lay a book flat on top of your head and mark the wall under it.
- Measure from the seat surface to the mark. Measure your standing height the same way, barefoot.
What the numbers mean
Your leg length here is height minus sitting height, the part of you below the seat. The leg to torso ratio divides it by sitting height, which includes the head and neck. The sitting height ratio is sitting height as a percentage of height; anthropologists use it to compare body proportions (Bogin & Varela-Silva, 2010). A lower sitting height ratio means relatively longer legs.
What is normal?
The US Army's ANSUR II survey measured 4,082 men and 1,986 women in 2012. From its public data:
| Men | Women | |
|---|---|---|
| Average height | 175.6 cm | 162.8 cm |
| Average sitting height | 91.8 cm | 85.7 cm |
| Sitting height ratio, average | 52.3% | 52.6% |
| Middle 90% (5th–95th percentile) | 50.0–54.4% | 50.2–54.8% |
| Leg to torso ratio, average | 0.91 | 0.90 |
Populations differ more than individuals in one group: average sitting height ratios range from about 47–48% in Australian Aboriginal adults, the relatively longest legs, to 54.6% in Guatemalan Maya men and 55.8% in Peruvian women (Bogin & Varela-Silva). Soldiers are not a random sample of the population, so treat the averages as a guide.
How leg lengthening changes it
For the average man above (175.6 cm, sitting height 91.8 cm), lengthening adds only to the legs:
| Leg gain | Height | Sitting height ratio | Leg to torso ratio |
|---|---|---|---|
| None | 175.6 cm | 52.3% | 0.91 |
| +5 cm | 180.6 cm | 50.8% | 0.97 |
| +8 cm | 183.6 cm | 50.0% | 1.00 |
| +10 cm | 185.6 cm | 49.5% | 1.02 |
An 8 cm gain takes him from the middle of the range to its long-legged end. See the same change on your own photo in the limb lengthening simulator, which measures your legs from the hip joint instead of the seat.