How many reps should I do to build muscle?

A much wider range than the usual answer. Over twelve weeks, trained men doing 20 to 25 reps with a light weight gained the same lean mass as trained men doing 8 to 12 with a heavy one. Both fiber types grew equally. The catch is that every set in that study went to failure.

Is 6 to 12 reps the best range for muscle growth?

It is a good default, but not for the reason usually given. There is no magic in those numbers. What that range does is let you grow without having to push every set to failure, while still getting decent strength, which is why it survives as general advice.

Can you build muscle with light weights?

Yes, with one condition and one limit. The condition is effort: at about 30% of your max, sets taken to failure grew the muscle 7.8% while sets stopped short grew it 2.8%, which was not a real change. The limit is that around 20% of your max underperformed everything above it.

How light is too light?

Somewhere around 20% of your one-rep max. In a study running 20, 40, 60 and 80% with the work matched, the thigh grew 8.9% at 20% and about 20% at all three heavier loads. Forty, sixty and eighty were indistinguishable from each other.

Do I have to go to failure?

It depends entirely on the weight, which is the part nobody mentions. With a heavy load at 80% of your max, going to failure added nothing: 8.1% growth against 7.7%. With a light load at 30%, failure was the difference between growing and not.

How many reps for strength rather than size?

Fewer and heavier, and here the traditional advice holds up. In the same study, the two heavy conditions raised the one-rep max by about 33% and the two light conditions by about 16 to 18%. Roughly double the strength gain for heavy work.

Does the rep range change once I am experienced?

The evidence here says not much. The study with trained men and the studies with untrained men reached the same conclusion about load and size. Experience changes how heavy you need to go for strength more than it changes the range that grows muscle.

Is 3 sets of 10 reps enough to build muscle?

Yes, provided the weight is heavy enough to make ten reps genuinely hard. Ten reps sits in the middle of the range that worked in every study here, so the reps are not the thing to worry about. The load is.

Is 3 sets of 15 reps enough to build muscle?

Yes, with a condition. Fifteen reps means a lighter weight, and light sets only worked when they were taken to the point of failure. At about 30% of maximum, sets taken to failure grew the muscle 7.8% and sets stopped short managed 2.8%.

Is 4 sets of 12 reps too much?

No. Twelve reps is well inside the effective range, and four sets is a normal amount of work rather than an excessive one. How many sets to do is really a separate question from how many reps, and it has its own answer on this site.

So what should I actually do?

Pick a weight between roughly a third and about 85% of your max. The lighter you go, the closer to failure you need to take the set. If you want strength as well as size, stay at the heavier end, because that is the one place the load genuinely decides the outcome.

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How many reps to build muscle

The range is wide. What matters is the load, and how hard you push a light one.

Last updated 25 August 2026

Every chart says the same thing. One to five reps for strength, six to twelve for size, fifteen or more for endurance. It has been printed for decades and it is presented as physiology. The middle row is the one that does not survive testing.

The short version

The question	The answer
What rep range builds muscle	Roughly 6 to 30, on the same terms.
What is too light	Around 20% of your max underperformed.
Does a light set need to reach failure	Yes. It is the difference between 7.8% and 2.8%.
Does a heavy set need to	No. 8.1% against 7.7%, so it made no difference.
What about strength	Heavy wins, by roughly double.

The range is far wider than twelve

In 2016 Robert Morton's group took 49 men who already trained and put them through twelve weeks of whole-body lifting. One group used a light weight, about 30 to 50% of their maximum, for 20 to 25 reps a set. The other used 75 to 90% for 8 to 12.

Both groups got bigger. Lean mass rose in both. Type I and type II fibers both grew. There was no significant difference between them on any of it.

Strength was the exception, and only partly. Every lift improved in both groups, but bench press was the one where the heavy group pulled clearly ahead, gaining 14 kg against 9 kg.

That study is usually summarized as "load does not matter for muscle growth". That summary is wrong, and the reason it is wrong is the most useful thing on this page.

The clause everybody drops

Every single set in Morton's study was taken to the point where another rep was impossible. It is stated plainly in the methods and it is doing all the work.

In 2022 Thiago Lasevicius's group tested exactly that. Twenty-five men, eight weeks, one leg per protocol, with the total work matched across all four conditions.

Load and effort	Muscle growth	Strength gain
30% of max, to failure	7.8%	17.7%
30% of max, stopping short	2.8%, not a real change	15.8%
80% of max, to failure	8.1%	33.8%
80% of max, stopping short	7.7%	33.4%

Read the first two rows and then the last two. With a light weight, whether you reach failure is the difference between growing and not growing. With a heavy weight, it makes no difference at all.

That is the rule, and it is not on any chart. A high rep count works, but it costs you something that a heavy set does not ask for.

The companion question, how close to failure a set should go and what that costs you within a session, is on the page about training to failure.

There is a floor, and it is around a fifth of your max

The range is wide but it is not open-ended. An earlier study from the same group ran four loads with the work matched: 20, 40, 60 and 80% of maximum.

Thigh muscle grew 8.9% at 20%, then 20.5%, 20.4% and 19.5% at the three heavier loads. The arm showed the same shape: 11.4% at 20%, then about 25% at each of the others.

Forty, sixty and eighty were indistinguishable from one another. Twenty was clearly worse. So there is a genuine bottom to the useful range, and it sits somewhere between a fifth and two fifths of your maximum.

Where the old advice is right

For strength, the traditional answer holds. Look again at the right-hand column above: about 33% for the heavy conditions and about 16 to 18% for the light ones, regardless of effort. Roughly double.

A meta-analysis by Brad Schoenfeld's group in 2016 had already pointed this way, finding trends favoring heavy loads for both strength and size. Neither trend reached significance, and the authors were careful about why: there were too few studies at the time. The trials since have confirmed the strength half and undercut the size half.

What to actually do

Pick a weight somewhere between roughly a third and 85% of your maximum. Inside that range, the number of reps is mostly a preference.

Two things decide which end suits you.

The lighter you go, the closer to failure each set has to be. At the light end there is no such thing as an easy productive set.
If you want strength as well as size, stay heavy. That is the one outcome where the load genuinely decides the result.

Whichever end you pick, you need a record of the weight to know it is going up. The workout builder logs each set against a load, and how many sets per exercise covers the third variable these studies deliberately held still.

How to read this evidence

All four sources are men only or nearly so, which makes this the most male-skewed page in this library.

Two of the four also trained one limb one way and the other limb another way. That is a clean method for isolating the effect of load, and it is not how anyone actually trains. Treat the numbers as a comparison between conditions rather than as what to expect from a real training block.

Common questions

How many reps should I do to build muscle?: A much wider range than the usual answer. Over twelve weeks, trained men doing 20 to 25 reps with a light weight gained the same lean mass as trained men doing 8 to 12 with a heavy one. Both fiber types grew equally. The catch is that every set in that study went to failure.
Is 6 to 12 reps the best range for muscle growth?: It is a good default, but not for the reason usually given. There is no magic in those numbers. What that range does is let you grow without having to push every set to failure, while still getting decent strength, which is why it survives as general advice.
Can you build muscle with light weights?: Yes, with one condition and one limit. The condition is effort: at about 30% of your max, sets taken to failure grew the muscle 7.8% while sets stopped short grew it 2.8%, which was not a real change. The limit is that around 20% of your max underperformed everything above it.
How light is too light?: Somewhere around 20% of your one-rep max. In a study running 20, 40, 60 and 80% with the work matched, the thigh grew 8.9% at 20% and about 20% at all three heavier loads. Forty, sixty and eighty were indistinguishable from each other.
Do I have to go to failure?: It depends entirely on the weight, which is the part nobody mentions. With a heavy load at 80% of your max, going to failure added nothing: 8.1% growth against 7.7%. With a light load at 30%, failure was the difference between growing and not.
How many reps for strength rather than size?: Fewer and heavier, and here the traditional advice holds up. In the same study, the two heavy conditions raised the one-rep max by about 33% and the two light conditions by about 16 to 18%. Roughly double the strength gain for heavy work.
Does the rep range change once I am experienced?: The evidence here says not much. The study with trained men and the studies with untrained men reached the same conclusion about load and size. Experience changes how heavy you need to go for strength more than it changes the range that grows muscle.
Is 3 sets of 10 reps enough to build muscle?: Yes, provided the weight is heavy enough to make ten reps genuinely hard. Ten reps sits in the middle of the range that worked in every study here, so the reps are not the thing to worry about. The load is.
Is 3 sets of 15 reps enough to build muscle?: Yes, with a condition. Fifteen reps means a lighter weight, and light sets only worked when they were taken to the point of failure. At about 30% of maximum, sets taken to failure grew the muscle 7.8% and sets stopped short managed 2.8%.
Is 4 sets of 12 reps too much?: No. Twelve reps is well inside the effective range, and four sets is a normal amount of work rather than an excessive one. How many sets to do is really a separate question from how many reps, and it has its own answer on this site.
So what should I actually do?: Pick a weight between roughly a third and about 85% of your max. The lighter you go, the closer to failure you need to take the set. If you want strength as well as size, stay at the heavier end, because that is the one place the load genuinely decides the outcome.

Where these numbers come from

Four papers, all in healthy adults, each read in full before anything here was written.

Morton RW, Oikawa SY, Wavell CG, Mazara N, McGlory C, Quadrilatero J, Baechler BL, Baker SK, Phillips SM (2016). Neither load nor systemic hormones determine resistance training-mediated hypertrophy or strength gains in resistance-trained young men. Journal of Applied Physiology 121(1):129-38. PMID 27174923. The 49 trained men, and the bench press difference.
Lasevicius T, Schoenfeld BJ, Silva-Batista C, Barros TS, Aihara AY, Brendon H, Longo AR, Tricoli V, Peres BA, Teixeira EL (2022). Muscle failure promotes greater muscle hypertrophy in low-load but not in high-load resistance training. Journal of Strength and Conditioning Research 36(2):346-351. PMID 31895290. The four-protocol table above.
Lasevicius T, Ugrinowitsch C, Schoenfeld BJ, Roschel H, Tavares LD, De Souza EO, Laurentino G, Tricoli V (2018). Effects of different intensities of resistance training with equated volume load on muscle strength and hypertrophy. European Journal of Sport Science 18(6):772-780. PMID 29564973. The floor at 20%.
Schoenfeld BJ, Wilson JM, Lowery RP, Krieger JW (2016). Muscular adaptations in low- versus high-load resistance training: a meta-analysis. European Journal of Sport Science 16(1):1-10. PMID 25530577. The earlier trends, and the authors' own caution about them.

What this page does not claim: that load does not matter, that light training is as good for strength, or that one rep number is best. Morton's result holds only because every set went to failure. Strength was consistently better with heavier loads. The evidence supports a range with two conditions rather than a number.

If a lift hurts rather than being hard, stop and see a physiotherapist.