How to Estimate Your One-Rep Max Safely

You can estimate your one-rep max (1RM) by lifting a submaximal weight for a few clean reps and running the result through a formula like Epley or Brzycki. For most people this is safer and nearly as useful as grinding out an actual single, and it is the more practical choice for everyday training.

This article covers why estimating usually beats testing, the main prediction formulas and their equations, how accuracy falls apart at high rep counts, and how to turn an estimated 1RM into training percentages you can program around.

Why Estimate Instead of Testing a True 1RM

A true 1RM test means loading a bar with the most weight you can lift exactly once. That has real value for competitive lifters, but it carries costs that often outweigh the benefit for everyone else.

• Injury risk. A maximal attempt pushes joints, connective tissue, and technique to their limits, where form tends to break down first.
• Fatigue and recovery. A genuine max effort is taxing and can compromise the rest of a training session or week.
• Skill dependence. Hitting a true max requires practice at maximal lifting itself; an undertrained lifter may fail a weight they could actually move, simply from inexperience or nerves.
• Spotting requirements. Safely testing a max on lifts like the bench press requires competent spotters or safety equipment.

An estimate sidesteps most of this. You take a weight you can handle for, say, three to eight solid reps, stop with a rep or two still in the tank, and let a formula extrapolate the single. The trade is a small loss of precision for a large gain in safety and convenience.

The Main Estimation Formulas

Several formulas exist, all built by fitting the relationship between reps and load across many lifters. The three most common are Epley, Brzycki, and Lombardi. In the equations below, w is the weight lifted and r is the number of reps completed.

• Epley: 1RM = w × (1 + r ÷ 30). Equivalently, w + w × r × 0.0333.
• Brzycki: 1RM = w × 36 ÷ (37 − r).
• Lombardi: 1RM = w × r^0.10 (the weight times reps raised to the power 0.10).

These disagree slightly. Epley and Brzycki happen to give the same answer at exactly 10 reps and diverge on either side: Brzycki tends to read a touch lower at high reps, Epley a touch higher. Lombardi behaves differently again because of its exponential form. No single formula is universally "correct," so many calculators average several or let you pick.

A worked example: a lifter who presses 100 kg for 5 reps gets an Epley estimate of 100 × (1 + 5 ÷ 30) ≈ 117 kg, and a Brzycki estimate of 100 × 36 ÷ 32 ≈ 113 kg. The few-kilogram gap between formulas is normal and small relative to the day-to-day variation in your actual strength.

Why Accuracy Degrades Above About 10 Reps

These formulas are most accurate in the low-rep range, roughly 2 to 10 reps, and they drift as the rep count climbs.

The reason is physiological. At low reps, performance is limited mainly by maximal force production, which is what a 1RM measures. As reps increase past 10 or so, muscular endurance and fatigue resistance start to dominate, and those qualities vary enormously between people. Two lifters with an identical true 1RM might manage very different numbers of reps at 60% of it, because one has more endurance. A formula cannot see that difference, so its extrapolation gets shakier.

Practically: estimate from a set in the 3-to-8-rep range whenever possible. A set of 20 might tell you more about your conditioning than your max strength, and any 1RM derived from it should be treated with heavy skepticism.

Reps to Percentage of 1RM

The flip side of these formulas is a rep-to-percentage chart. It answers the everyday question: roughly what percentage of my 1RM can I lift for a given number of reps? The table below reflects commonly used averages.

Read it both directions. If you lifted a weight for 5 reps, that weight is about 87% of your 1RM, so your max is roughly the weight divided by 0.87. These are population averages; your personal numbers may run higher or lower, especially at the high-rep end.

Programming With an Estimated 1RM

Most structured strength programs prescribe load as a percentage of 1RM, which is exactly what an estimate gives you. Once you have a working 1RM, you can map intensity to goal:

A few practical guidelines keep this honest. Re-estimate periodically rather than once, since your 1RM moves as you train. Use a slightly conservative estimate for programming, so prescribed weights stay achievable on bad days. And remember that estimates are lift-specific: your bench, squat, and deadlift each need their own.

The Bottom Line

Estimating your 1RM from a submaximal set is safer than maxing out, fast to do, and accurate enough for programming when you keep the test set to roughly 3 to 8 reps. The Epley, Brzycki, and Lombardi formulas will give slightly different numbers, all of them approximations rather than guarantees. Use the estimate as a planning anchor, revisit it as you get stronger, and leave true maximal testing to situations that genuinely call for it. None of this replaces individualized coaching or medical guidance if you are training around an injury.