1RM calculator: Epley, Brzycki and a percentage table you can train with

The two formulas, side by side

Both equations turn a submaximal set into an estimated maximum. They start from the same idea: the more repetitions you can do with a load, the further that load sits below your maximum.

• Epley multiplies the load by one plus the repetitions divided by thirty. It circulates widely in coaching, although we could not trace it to a peer-reviewed paper.
• Brzycki divides the load by a factor that shrinks as repetitions rise. Matt Brzycki published it in 1993 in the Journal of Physical Education, Recreation and Dance. The version used here is the one commonly reproduced: load multiplied by 36, divided by 37 minus the repetitions.

Take a set of 5 repetitions at 70 kilograms on a bench press. Epley gives about 81.7 kilograms, Brzycki about 78.8. The calculator shows both and uses their average, about 80.2 kilograms, as the working estimate.

The two formulas agree closely between 3 and 6 repetitions and drift apart beyond 10. That divergence is itself a warning. When two respected equations disagree by several kilograms, neither is precise for your set.

Which formula is more accurate?

No study settles it. McNair and colleagues compared 12 equations on a knee-extension machine in 18 people with knee osteoarthritis. Epley, Brzycki and several others were among the best, with typical errors of 3 to 4%. On a leg press, other equations did better. LeSuer and colleagues compared prediction equations for the bench press, squat and deadlift in 1997.

The honest reading is that the exercise matters as much as the formula. Showing both results lets you see the spread instead of trusting a single figure to the decimal.

Reading the percentage table

Below the estimate, the calculator lists eight loads, from 95% to 60% of your maximum, each with a typical number of repetitions. Those repetition counts are not measurements. They come from inverting the Brzycki relation, so they are arithmetic, not a study result.

Real people deviate from them, for two reasons.

• The exercise changes the count. Shimano and colleagues found that at 60% of the maximum, people managed more repetitions on the back squat than on the bench press or the arm curl. The amount of muscle involved matters.
• Individuals differ. A 2024 meta-regression by Nuzzo and colleagues, covering 269 studies and 7,289 people, built separate tables for the bench press and the leg press because the leg press allowed more repetitions across the loading range. Sex, age and training status had little influence, but the spread between individuals was real.

Use the table to choose a first load. Then let the set correct it: if the last two repetitions at 80% feel easy, the load is light for you on that exercise.

Turning the estimate into a week of training

The American College of Sports Medicine expresses its advice in repetition maximums rather than percentages. Its 2009 position stand recommends loads of 8 to 12 repetition maximum for novices. Intermediate and advanced lifters use 1 to 12 repetition maximum in a periodised way, with eventual emphasis on heavy loading of 1 to 6 repetition maximum and 3 to 5 minutes of rest.

For a busy adult with two strength sessions a week, a sensible starting point looks like this.

1. Estimate the maximum on each main lift from a set of about 5 repetitions.
2. Train most sets with a load you can lift 8 to 12 times with clean form.
3. Once a load allows one or two repetitions beyond the target, add 2 to 10%, as the ACSM position stand advises.
4. Recalculate the maximum every four to six weeks from a fresh set of about 5. That rhythm is a coaching habit, not a rule from a study.

For endurance of the muscle, the same position stand describes light to moderate loads of 40 to 60% of the maximum for more than 15 repetitions, with rests under 90 seconds. That is a different goal from the strength work above, and the calculator's table stops at 60% for that reason.

The choice of load also depends on what you want. Schoenfeld and colleagues found that heavy loads gave larger gains in maximal strength, while muscle growth was similar with light or heavy loads. A coach chasing a heavier lift and one chasing muscle tone will read the same table differently. The broader programme is set out in strength training for executives, and the movements themselves in ten essential movements.

Why estimate rather than test

A measured maximum is a reliable number. A 2020 review by Grgic and colleagues pooled 32 studies and 1,595 people: the median test-retest correlation was 0.97 and the median variation 4.2%, including in older and untrained people. Levinger and colleagues found that untrained adults around 51 years old needed only one familiarisation session and one test session to get a reliable result.

So the issue is not that a true test is inaccurate. It is that it asks for a supervised warm-up, a spotter or safety pins, and a day when you are fresh. We found no verified data on injury rates during maximal tests in middle-aged adults, so we make no claim either way. For most people who train for health, an estimate from 3 to 10 repetitions answers the practical question, which load to use next week, at much lower demand.

When the number misleads

Three situations make the estimate less useful.

• More than 10 repetitions. The calculator flags it. Reynolds found that load falls nonlinearly as repetitions rise, so formula error grows.
• Poor technique on the last repetitions. A set finished with a rounded back or a bounce off the chest overstates what you can do with control.
• A bad day. After a short night or a long flight, the same load feels heavier. Read the estimate across several weeks rather than from one session. The recovery guide explains how sleep and load interact.

Estimate from a set of 3 to 10 repetitions with clean technique, and use a spotter or safety pins on the bench press and squat. If you have uncontrolled blood pressure, heart disease, a recent injury or pain, ask your doctor before any heavy lifting.

Tracking it over months

The estimated maximum is most valuable as a trend. Write down the load, the repetitions and the date for each main lift. If the estimate rises over two or three months while your sets stay clean, the programme is working. If it stalls, look at sleep, at the number of sessions you actually kept and at the load progression before changing exercises. After 40, a slow but steady rise is a good result, as strength after 40 explains.

The coaches of the Club record the load and repetitions of each set in the report they send after the session, so the trend builds itself. You can create your space with one email.