What is a one-rep max?
Your one-rep max (1RM) is the heaviest weight you can lift for one complete repetition with good form. It is the standard measure of maximal strength, and many training programs prescribe loads as a percentage of it, for example “5 sets of 5 at 80%”.
Testing a true max is tiring and carries more risk. A 1RM calculator estimates it from a lighter set you have already done.
How the calculator works
The heavier a weight is relative to your max, the fewer reps you can do with it. Researchers have turned that relationship into prediction equations. Our main estimate blends the two most widely used:
We average the share of your max each formula predicts for your rep count, which keeps the estimate and the rep-max table consistent with each other. For a single rep, your 1RM is simply the weight you lifted.
Using percentages in your training
| % of 1RM | Typical reps | Common use |
|---|---|---|
| 90–100% | 1–4 | Maximal strength, peaking |
| 80–90% | 4–8 | Strength and muscle |
| 65–80% | 8–15 | Muscle growth |
| Below 65% | 15+ | Muscular endurance, technique |
Muscle growth happens across a wide range of loads, as long as sets are taken close to failure. Heavier loads build more maximal strength. Most well-designed programs use a mix. The tables under the calculator give you the exact weights for your numbers.
How to get the most accurate estimate
- Use a hard set. Enter a set where you could have done at most one or two more reps.
- Keep reps under 10. Estimates from sets of 3–6 reps are the most reliable.
- Use a recent set. Strength changes quickly, especially for newer lifters.
- Keep the form strict. Bounced or half reps inflate the estimate.
Loading the bar
The calculator shows the plates to load for your estimated max on a standard 20 kg (45 lb) barbell, using competition plate colours. The weight is rounded down to the nearest load you can make with standard plates.
Research behind this calculator
- LeSuer DA et al. (1997). The accuracy of prediction equations for estimating 1-RM performance in the bench press, squat, and deadlift. Journal of Strength and Conditioning Research.
- Schoenfeld BJ et al. (2017). Strength and hypertrophy adaptations between low- vs. high-load resistance training. Journal of Strength and Conditioning Research.
Last updated September 21, 2026.