How much muscle can you build without drugs?

Short answer

Most topped out around 81 kg of lean mass at 180 cm tall (a lean-mass-for-height index of 25). Some went past 25, so it is not a drug test line but the ceiling most people reach.

How much muscle can you build without drugs?
'Muscle ÷ height² = 25 is the natural limit' — does this formula hold?
A common claim says that if your fat-free mass index (lean mass, meaning muscle and everything except fat, divided by height squared) goes above 25, you must be on drugs. We checked where this number came from and whether it holds up.
The number 25 came from 157 men in 1995
The 74 who never used drugs stopped at 25.0
Researchers compared the index of 74 people who did not use steroids and 83 who did, adjusted to a height of 180 cm. Nobody in the non-user group went above 25.0. Many steroid users easily passed 25, and some went above 30.
The best bodies before drugs were similar
20 Mr. America winners from 1939 to 1959 averaged 25.4
The same study estimated the index of 20 Mr. America winners from 1939 to 1959, before steroids spread. Their average was 25.4. The top physiques of that era also clustered around 25.
Today's natural pros were also below 25
6 pros averaged 23.8 on competition day
Among 11 people measured on competition day at a natural federation (WNBF) show, the 6 pros averaged 23.8 and the 5 amateurs 22.8. Among 596 men on US college sports teams, the average was 21.5.
But 25 was not a wall you cannot pass
4% of 235 college football players were above 25
Adjusted to a height of 180 cm, 62 of 235 college football players (26.4%) were above 25. This study did not check for drug use. Among 11 natural competitors, 5 also passed another proposed natural limit (muscle-to-bone ratio of 5.2).
How far you can grow varied hugely between people
The same 12 weeks of training gave -2% to +59%
When 585 people trained one arm the same way for 12 weeks, the change in upper-arm muscle size ranged from -2% to +59%. With the same training, how much muscle people gained varied hugely.
Bottom line: most people stop around 25
At 180 cm tall, about 81 kg of lean mass
Drug-free bodies clustered at an index of about 23 to 25 for a 180 cm height, which is about 75 to 81 kg of lean mass. Going from the college-athlete average (21.5) to 25 is a gap of about 11 kg. Read 25 as the ceiling most people reach, not a line that proves drug use.