What is a one-rep max (1RM)?

Your one-rep max is the heaviest weight you can lift for a single repetition of an exercise with good form. It is the standard reference for strength and for setting training loads. Rather than testing it directly every time, you can estimate it from a lighter set taken close to failure — for example a weight you lifted for 5 reps — using a prediction formula.

How is 1RM estimated from reps?

Two common formulas are Epley, 1RM = weight × (1 + reps ÷ 30), and Brzycki, 1RM = weight × 36 ÷ (37 − reps). For 100 kg lifted 5 times, Epley gives 100 × (1 + 5/30) ≈ 116.7 kg and Brzycki gives 100 × 36/32 = 112.5 kg, averaging about 114.6 kg. They agree closely at low reps and drift apart as reps rise.

How many reps give the best estimate?

Estimates are most accurate for sets of roughly 10 reps or fewer taken close to failure. Beyond about 10–12 reps, fatigue and endurance factors make the prediction less reliable, and the formulas tend to overestimate. For the closest estimate, use a heavy set of 3–6 reps performed with solid technique.

How do I use 1RM to program training?

Training loads are set as a percentage of 1RM. As a rough guide: about 100% for 1 rep, 95% for 2, 90% for 4, 85% for 6, 80% for 8, 75% for 10 and 70% for 12. Strength work tends to use higher percentages for low reps, while hypertrophy work uses moderate percentages for more reps. Adjust based on how the sets actually feel.

Is it safe to test my true 1RM?

Testing an actual 1RM is demanding and carries injury risk if done carelessly. Always warm up thoroughly, use good technique, and have a spotter or safety bars. Beginners are usually better served by estimating 1RM from submaximal sets and training below maximal loads. This calculator is an estimate for programming, not medical or coaching advice.

One Rep Max Calculator — estimate your 1RM

% of 1RM	Approx. reps
100%	1
90%	4
80%	8
70%	12

Your one-rep max is the most you can lift once with good form, and it anchors strength programming. Instead of testing it directly each time, you can estimate it from a heavier set taken near failure. Two formulas dominate: Epley (1RM = weight × (1 + reps/30)) and Brzycki (1RM = weight × 36/(37 − reps)). They agree closely for low reps and diverge as reps climb, so they're most trustworthy for sets of about ten or fewer. From the 1RM you set working weights as percentages.

Reviewed: June 20, 2026 · Author: Naveen P N, Founder — AI Calculator · Verified against: the Epley and Brzycki 1RM formulas. Not medical advice.

The 1RM formulas

Epley

1RM = weight × (1 + reps / 30)

Brzycki

1RM = weight × 36 / (37 − reps)

Training load

working weight = 1RM × target % (e.g. 80% for ~8 reps)

Both formulas inflate the lifted weight by an amount that grows with reps — a set of 5 implies a higher single than a set of 2 at the same weight. Epley scales linearly with reps, while Brzycki uses a ratio that rises faster as reps approach the high teens (where it breaks down, since the denominator shrinks). Averaging the two is a sensible working estimate. Percentages then convert the 1RM into daily training loads for strength or hypertrophy.

Worked example — 100 kg for 5 reps

Scenario: you lift 100 kg for 5 solid reps.

Epley

100 × (1 + 5/30) = 100 × 1.1667 ≈ 116.67 kg

Brzycki

100 × 36 / (37 − 5) = 100 × 36/32 = 112.5 kg

Epley estimates about 116.7 kg and Brzycki 112.5 kg, so a sensible working 1RM is the average, roughly 114.6 kg. From there, 85% (a common strength-day load) is about 97 kg, 80% about 92 kg, and 90% about 103 kg. The two formulas sit within a couple of kilos here because 5 reps is well inside their reliable range; push the rep count toward 15+ and the spread widens, which is why heavy sets of 3–6 reps give the cleanest estimate.

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Frequently Asked Questions

What is a 1RM?⌄

The heaviest weight you can lift once with good form — the reference for strength and loads.

How is it estimated?⌄

Epley w×(1+reps/30) or Brzycki w×36/(37−reps). 100×5 → 116.7 / 112.5.

Best rep range?⌄

≤ 10 reps near failure; 3–6 reps gives the closest estimate. High reps overestimate.

How do I program with it?⌄

% of 1RM: ~100% 1 rep, 90% 4, 80% 8, 70% 12. Higher % for strength, moderate for size.

Is testing a true 1RM safe?⌄

Only with a warm-up, good form and a spotter. Beginners should estimate and train submaximally.

One Rep Max Calculator

One-rep max — Quick answer