How the 1RM estimate works
The heavier the weight, the fewer times you can lift it. Strength coaches have built formulas from this relationship that predict your single-rep max from a set of several reps.
Epley: 1RM = weight × (1 + reps ÷ 30)
Brzycki: 1RM = weight × 36 ÷ (37 − reps)
Worked example
You bench press 200 lb for 5 reps.
- Epley: 200 × (1 + 5 ÷ 30) ≈ 233 lb
- Brzycki: 200 × 36 ÷ 32 = 225 lb
- Average estimate: about 229 lb
Using percentages in training
Many programs set training weights as a percentage of your 1RM. Heavier percentages with low reps build maximal strength, while moderate percentages with more reps build muscle and work capacity. The chart above shows the weight for each percentage and roughly how many reps that weight allows.
Tips for safe lifting
- Warm up with lighter sets before heavy work.
- Use a spotter or safety bars for bench press and squats.
- Count only reps done with good form.
- Re-test every few weeks as you get stronger.
This calculator gives estimates for general fitness use and is not medical advice.
Last reviewed October 2026.
Frequently asked questions
What is a one rep max?
Your one rep max (1RM) is the most weight you can lift for a single repetition of an exercise with good form. It is used to measure strength and to set training weights as percentages.
How is 1RM estimated from reps?
Formulas use a weight you lifted for several reps to predict your single-rep max. This calculator shows the Epley formula, weight × (1 + reps ÷ 30), and the Brzycki formula, weight × 36 ÷ (37 − reps), plus their average.
How many reps should I use for the estimate?
Estimates are most accurate from sets of about 2 to 10 reps. With very high reps, endurance plays a bigger role and the prediction becomes less reliable.
Is it safer to estimate than to test a true max?
For many lifters, yes. Estimating from a set of several reps avoids lifting a maximal weight, which carries more injury risk. If you do test a true max, warm up well and use a spotter or safety bars.
What weight should I use for training?
Programs often prescribe percentages of 1RM, for example around 70–85% for sets in the 5 to 12 rep range used for building strength and muscle. The table shows the weights for common percentages.