One Rep Max Calculator

What is a one-rep max calculator?

Your one-rep max (1RM) is the heaviest weight you can lift for a single rep with good form. This 1RM calculator estimates it from any hard set of 1–15 reps — no risky max-out session required — and gives you the percentage chart that most strength programs are written in.

How it works

We compute two of the most validated prediction equations and average them:

• Epley (1985): 1RM = weight × (1 + reps ÷ 30)
• Brzycki (1993): 1RM = weight × 36 ÷ (37 − reps)

The two agree almost exactly at low reps and diverge slightly as reps climb; averaging them smooths the difference. Research comparing prediction equations finds accuracy within a few percent for sets of up to about 10 reps, with error growing beyond that — which is why the calculator caps at 15.

Frequently asked questions

How accurate is an estimated 1RM?

Within 2–5% for most lifters when using a 3–8 rep set taken close to failure. The estimate is least reliable for very high reps and for lifts with big technique demands — a deadlift 1RM estimated from 12 reps is a guess, not a measurement.

Do I ever need to test a true 1RM?

Only if you compete in powerlifting. For programming purposes, estimated maxes work — and testing singles frequently costs recovery that training could use. If you do max out, use a spotter and warm up thoroughly.

What percentage should I train at?

Roughly: 85%+ builds maximal strength (1–5 reps), 70–85% builds muscle and strength (6–12 reps), 55–70% suits volume and technique work. The table above maps each percentage to typical reps.

References

1. Epley B. Poundage chart. In: Boyd Epley Workout. University of Nebraska; 1985.
2. Brzycki M. Strength testing — predicting a one-rep max from reps-to-fatigue. JOPERD. 1993;64(1):88–90.
3. Mayhew JL, et al. Muscular endurance repetitions to predict bench press strength in men of different training levels. J Sports Med Phys Fitness. 1995;35(2):108–113.

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