How many hours of sleep do you need to build muscle?

Short answer

Seven to eight hours a night is enough. A few nights in a row of 6 hours or less slowed muscle building and cut strength, but sleeping past 8 hours did nothing extra for muscle.

How many hours of sleep do you need to build muscle?
'More sleep → more muscle' — does this formula hold?
People often say muscle grows while you sleep, so the longer the better. But how short is too short, and how much is enough? We checked studies that changed people's sleep directly and surveys of tens of thousands of people.
Five nights of 4 hours?
Muscle building slowed by about 19%
24 people were split into three groups and spent either 8 or 4 hours in bed each night for 5 nights. Everyone ate exactly the same food. In the 4-hour group, the rate of building new muscle protein was 1.24% per day, about 19% lower than the 8-hour group (1.53%).
Strength and performance drop too
Sleeping 6 hours or less cut performance by 7.56% on average
An analysis that pooled 69 studies and 959 people found that exercise performance fell by 7.56% on average after 6 hours of sleep or less. It dropped for strength, power and endurance alike. Each 1 extra hour awake before exercise cut performance by about 0.4% more.
So is one short night a problem?
The problem was several nights in a row
An analysis of 17 studies found that several nights in a row of short sleep reduced strength in lifts that use many joints, like the squat. An analysis pooling 252 people found that cutting sleep by a few hours did not meaningfully lower testosterone; it dropped only after going 24 hours or more with no sleep at all.
Then is more sleep always better?
Past 8 hours, the risk of muscle loss rose again
An analysis pooling 17,551 people found that those sleeping under 6 hours had a 1.71 times higher risk of sarcopenia (age-related muscle loss) than those sleeping 6 to 8 hours, and those sleeping over 8 hours had a 1.52 times higher risk. The lowest risk was at 8 hours a day.
At ages 20 to 59, quality mattered more than hours
Poor sleepers had 1.72 times the risk of low muscle
A survey of 7,187 people aged 20 to 59 found that sleeping under 6 hours or over 8 hours did not raise the risk of having low muscle. But people who had trouble sleeping or sleep problems had a 1.72 times higher risk of low muscle.
What if you add back missing sleep?
About 1 hour 50 minutes more a night improved results
11 people spent at least 10 hours in bed each night for 5 to 7 weeks, and their actual sleep rose by 110.9 minutes a night. Their sprint time dropped from 16.2 to 15.5 seconds, and basketball free throw accuracy rose by 9%. If you usually sleep too little, you gain from adding it back.
Bottom line: 7 to 8 hours is enough
Cutting nights of 6 hours or less matters more than sleeping longer
A few nights of 6 hours or less slowed muscle building and cut strength, and sleeping past 8 hours did not help more. Sleep experts also treat under 7 hours as short sleep, but say each person can sleep what they need rather than everyone fitting the same 7 to 9 hours.