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Tools/One-Rep Max Calculator

One-Rep Max Calculator

Your one-rep max (1RM) is the maximum weight you can lift for a single repetition. It is used to set training loads as a percentage of your max. Enter the weight you lifted and the number of reps you completed — this calculator applies three established formulas (Epley, Brzycki, and Lander) and shows their average so you get a reliable estimate without performing a true max effort.

About the formulas

Epley (1985): The most widely used formula. Tends to slightly overestimate at higher rep ranges but is accurate from 1–10 reps.

Brzycki (1993): Accurate for sets of 1–10 reps. Gives slightly more conservative estimates than Epley.

Lander: Uses a linear model that performs well across a broader rep range, especially 6–12 reps.

All formulas become less accurate above 10 reps. For the most reliable estimate, test with a weight you can lift for 3–6 reps.

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How the Calculation Works

A 1RM calculator converts a submaximal set — a weight you lifted for multiple reps — into an estimate of the most you could lift once. Every formula rests on the same observation: there is a predictable relationship between how much of your max you lift and how many reps you can perform with it. This calculator runs three of the most established equations and averages them.

Epley: 1RM = weight × (1 + reps ÷ 30)
Brzycki: 1RM = weight × 36 ÷ (37 − reps)
Lander: 1RM = 100 × weight ÷ (101.3 − 2.67123 × reps)

The Epley formula is the simplest and the most widely used; it adds roughly 3.3% of the bar weight per rep. Brzycki was derived from bench press data and tracks slightly lower at higher rep counts. Lander sits between the two. Below 6 reps all three agree within a couple of kilograms, which is why low-rep sets give the most trustworthy estimates.

A Worked Example

Say you bench press 100 kg for 5 reps. Epley gives 100 × (1 + 5/30) = 116.7 kg. Brzycki gives 100 × 36 ÷ 32 = 112.5 kg. Lander gives 100 × 100 ÷ 87.9 = 113.8 kg. The average — about 114 kg — is your working estimate. Notice the spread is only ~4 kg across formulas; had you entered a 12-rep set instead, the spread would triple, which is exactly why testing with heavy triples or fives beats rep-out sets for accuracy.

Using Your 1RM in Training

Your 1RM is not a number to attempt in the gym every week — it is the anchor for percentage-based programming. Strength work typically lives at 80-92.5% of 1RM for 2-6 reps, hypertrophy work at 65-80% for 6-12 reps, and technique or speed work at 50-65%. The percentage chart above the fold maps your estimate to each of these zones.

Two practical tips. First, consider programming from a training max — 90% of your estimated 1RM — the way 5/3/1 does; it keeps bar speed high and leaves room to progress for months. Second, re-estimate at the end of each block from a recent hard set rather than grinding a true max single: an AMRAP at a known weight gives the formulas better input with far less injury risk.

Frequently Asked Questions

How accurate are 1RM calculators?+

For sets of 2-6 reps, formula estimates typically land within 2-5% of a tested max. Accuracy drops as reps climb — a 12-rep set says more about muscular endurance than maximal strength. For programming purposes, an estimate from a hard set of 3-5 reps is accurate enough.

Which 1RM formula is best — Epley, Brzycki, or Lander?+

They agree closely up to about 5 reps and diverge after. Epley tends to estimate slightly higher at high reps, Brzycki slightly lower. That is why this calculator shows all three plus an average — the average is the most robust single number to program from.

Do I need to actually test my one-rep max?+

No. Most training programs (5/3/1, GZCLP, most percentage-based plans) work perfectly well from an estimated 1RM — many even recommend using a conservative "training max" at 90% of your estimate rather than a true tested max.

How often should I recalculate my 1RM?+

Every 4-6 weeks, or at the end of each training block. Recalculate from a recent hard set rather than re-testing a true single — an AMRAP set at a known weight is safer and gives the formulas exactly the input they need.

Does the same 1RM formula work for every exercise?+

The formulas are most reliable for barbell compound lifts — squat, bench press, deadlift, overhead press. For isolation exercises and machines, rep-to-max relationships are less consistent, so treat the estimate as a rough guide.

Keep Going

One-Rep Max Guide

The full guide to estimating, testing, and programming with your 1RM.

5/3/1 Program Guide

The classic percentage-based program that runs entirely off your training max.

Progressive Overload

How to actually get stronger over time using your 1RM percentages.

AI Workout Generator

Get a percentage-based program built around your numbers in 60 seconds.