What is a 1RM, and why not test it directly
1RM (one-rep max) is the heaviest weight a client can lift once with good form. Training loads are based on it – for example, "3 sets of 8 at 75%." But testing a true max is needlessly risky and draining for most clients. It's much safer to estimate the max from a lighter set with more reps.
1RM calculator
Enter the weight and reps from a heavy set your client completed with good form.
The estimate is most accurate at 2–8 reps. At 10 reps or more, treat the result as a rough guide.
Sources: Epley (1985) and Brzycki (1993) formulas; accuracy tested e.g. in LeSuer et al., J Strength Cond Res 1997. Percentages and reps based on the NSCA %1RM table (approximate).
Percentages by client goal
The estimated max is just the starting point. Depending on what the client wants to achieve, you train in a different range of percentages and reps (roughly following NSCA guidelines):
- Strength – 85 % and above, 1 to 6 reps, 2 to 5 minutes rest.
- Muscle (size) – roughly 67 to 85 %, 6 to 12 reps, 30 to 90 seconds rest.
- Endurance and technique – under 67 %, 12 or more reps, short rest.
Pick a goal in the calculator and the chart highlights the weights that go with it.
How to get an accurate estimate
- 2 to 8 reps – the formulas are most accurate in this range. At 12 reps or more, the estimate becomes much less reliable.
- Close to failure – the set should end when the client has at most one more good rep left in the tank.
- After a warm-up – do 2 to 3 lighter sets first, not cold at the start of the session.
- Same exercise, same form – squat depth or touching the bar to the chest must be the same every time you measure.
How to use the percentage chart
The chart below the result shows loads for the common training zones. Strength work is usually done at 80–90%, muscle building at 65–80%, and technique practice and warm-ups at 50–65%. The rep counts are approximate – every client is a little different.
Repeat the estimate every 4 to 8 weeks. As the max goes up, so do the training loads – and your client can see they're making progress.
When percentages don’t fit: reps in reserve
Strength changes from day to day – sleep, stress and food all play a part. That’s why it helps to adjust the weight by how many reps the client still has left at the end of a set (RIR – reps in reserve). For example “8 reps, 2 in reserve”: if the client finds it easy, add weight; if they struggle, take some off. This approach is backed by research (e.g. Zourdos et al., 2016) and works for beginners too.
When to test a max and when not to
Don’t test a true max with beginners, older adults, clients after an injury or with high blood pressure. For them an estimate from a set of 5 to 8 reps is enough – that’s exactly what the calculator is for.
An advanced client can test their max when it makes sense (for example before a competition):
- Warm-up – several sets with rising weight, e.g. 50 % × 5, 70 % × 3, 80 % × 2, 90 % × 1.
- 3 to 5 attempts at the max, with 3 to 5 minutes rest between them.
- Always with a spotter and good technique – if technique breaks down, the attempt doesn’t count.
- Not after illness, when tired or at the start of a new program.
FAQ
Which formula is the best?
The calculator averages the two most widely used formulas, Epley and Brzycki. At low reps they give almost the same result; at higher reps they drift apart – the average is a sensible middle ground.
Does the estimate work for every exercise?
It works best for the big compound lifts – squat, bench press, deadlift, overhead press. It's less accurate for isolation exercises and machines.
Is it suitable for beginners?
Yes – that's exactly why you estimate the max. Beginners shouldn't test a single max rep; a set of 5 to 8 reps with good form is enough.
How often should I recalculate the max?
Every 4 to 8 weeks, always with the same exercise and the same technique. A rising number is great motivation, even for a client whose scale isn’t moving.
Why do I get a different max from 3 reps and from 12 reps?
The formulas are most accurate at low reps. At 10 or more reps endurance plays a part too, not just strength, so the estimate varies more.
