One Rep Max (1RM) Calculator

How this calculator works

You give it two numbers: the weight on the bar and the reps you got (1-15). It runs three classic prediction equations and averages them.

• Epley: weight × (1 + reps ÷ 30)
• Brzycki: weight × 36 ÷ (37 − reps)
• Lombardi: weight × reps^0.1

If you enter a single rep, the calculator simply returns that weight as your max. For anything else, the headline number is the plain average of the three. Example: 80 kg for 6 reps gives Epley 96 kg, Brzycki 92.9 kg and Lombardi 95.7 kg, so an estimated 1RM of about 94.9 kg.

The chart below the result multiplies that average by 60-100% and rounds each load to the nearest 2.5 kg, so it matches real plates (the plate calculator tells you exactly what to load). The “reps to failure” column runs Epley in reverse: 30 × (100 ÷ percentage − 1). That works out to about 5 reps at 85%, 8 at 80%, 10 at 75% and 20 at 60%.

Using your number in training

An estimated max is a planning tool. It is not a score to chase.

Most programs written in percentages (5/3/1, many powerlifting blocks, the free workout plans) need a 1RM to start. Plug in a recent hard set, pick your loads from the chart, and adjust after the first week. If 75% for 8 feels like a grinder, your estimate is probably high. Knock 2.5-5 kg off.

Pick a set that went close to failure with clean form. A set of 12 with three reps left in the tank will underestimate you, and a set where your hips shot up on the last rep will overestimate what you can do with good technique. For a set that deliberately stopped short, add your reps in reserve to the reps you did before entering it. Once you have the number, the RIR and RPE calculator turns it into working weights for any rep target.

Want to compare strength across body weights? Feed your estimated squat, bench and deadlift into the DOTS calculator. The trade-off between testing and estimating is covered in our guide to 1RM testing versus estimation equations.

Limitations and who it is not for

High reps make the formulas drift. In a study of 70 adults aged 18-69, 5RM tests predicted bench press and leg press 1RM better than 10RM or 20RM tests, and the authors advised using no more than 10 reps in linear equations (Reynolds et al., 2006). Work in 103 young women found the same pattern: predictions were more accurate from sets of fewer than 10 reps (Mayhew et al., 2008). The calculator flags any entry above 10 reps for this reason.

The exercise matters too. A small study of 16 men found more reps were possible at 60% of 1RM on the squat than on the bench press or arm curl (Shimano et al., 2006). One rep-to-percentage curve cannot fit every lift, so expect the chart to be less precise for high-rep work and for small isolation moves.

Beginners in their first few months will see their max move week to week, so recalculate often. Under-18s, anyone returning from injury, and anyone with heart disease or uncontrolled blood pressure should check with a doctor or physiotherapist before doing near-maximal sets at all.