One rep max calculator

What is a one rep max?

A one repetition maximum (1RM) is the most weight you can lift once, through the full movement, with good form. LeSuer and colleagues (1997) call the 1RM test the technique used most for measuring muscular strength. Exercise guidelines, such as the American College of Sports Medicine (ACSM) position stand by Garber and colleagues (2011), set training loads as a percentage of it.

Testing a true 1RM takes time and means handling a heavy weight. LeSuer and colleagues name both as concerns. Reynolds and colleagues (2006) add that age or an existing medical condition can make a maximal test unsafe for some people. That is why prediction formulas exist: you lift a lighter weight for as many repetitions as you can, and a formula turns the weight and the repetitions into an estimate.

Who this calculator is for

Anyone who lifts weights and wants a starting point for their training loads, without having to lift a maximal load. Physiotherapists and other clinicians can use it too, when they plan loading for a patient and a maximal lift is not needed or not safe.

How to use the one rep max calculator

1. Pick one exercise, such as a leg press or a bench press, and warm up with a light weight first.
2. Choose a weight you can lift at least once but no more than 10 times.
3. Lift it as many times as you can with good form. Count only full repetitions, and stop as soon as your form starts to break down.
4. Enter the weight in kg or lb, then the number of full repetitions.

The formulas assume the set went to fatigue, so that you could not have done another good repetition. If you stopped with repetitions in reserve, the estimate is likely to be too low. Rest well between hard sets. Reynolds and colleagues encourage a 5 minute rest between sets when testing a repetition maximum.

The Epley, Brzycki and Lombardi formulas

The calculator uses the three formulas as LeSuer and colleagues list them in their Table 1, where each one is written to predict the 1RM. In each one, "weight" is the weight you lifted and "reps" is the number of full repetitions.

Epley: 1RM = weight x (1 + 0.0333 x reps)
Brzycki: 1RM = 100 x weight / (102.78 minus 2.78 x reps)
Lombardi: 1RM = weight x reps to the power of 0.1

Epley's formula comes from a poundage chart in the Boyd Epley Workout (1985). Brzycki published his in a physical education journal in 1993. Lombardi's comes from his 1989 textbook. Reynolds and colleagues note that he gave no data showing how he developed it. They print the same Brzycki and Lombardi formulas and write the Epley factor as 0.033.

With 1 repetition, two of the formulas (Brzycki's and Lombardi's) give back the weight you lifted, while Epley gives 3.3% more. If you lifted a weight only once, that weight is already your measured 1RM for that day.

Why the calculator stops at 10 repetitions

LeSuer and colleagues describe these formulas as based on the link between the 1RM and the number of repetitions to fatigue, 10 or fewer, and they note that Brzycki found fewer than 10 repetitions worked better. Reynolds and colleagues list the guidance for the Brzycki and Epley formulas as fewer than 10 repetitions. So a 10 repetition set is the upper limit, and fewer is better.

Accuracy also drops as the number of repetitions rises. Reynolds and colleagues had 70 adults aged 18 to 69 lift their 1, 5, 10 and 20 repetition maximums on a barbell bench press and a leg press. The 5 repetition maximum predicted the 1RM best, and prediction got worse as the repetitions went up.

In a separate group of 20 people, the published formulas they tested with both 5 and 10 repetitions were all less accurate with the 10 repetition data. They concluded that no more than 10 repetitions should be used in linear equations, the group Epley and Brzycki belong to. Lombardi's formula was less accurate than the linear ones in their comparison.

If a heavier set is safe for you, a weight you can lift about 5 times will give a better estimate than one you can lift 10 times.

How accurate is an estimated 1RM?

It is an estimate, and its error depends on the exercise. LeSuer and colleagues tested 67 untrained college students (40 men and 27 women) on the bench press, using sets of 10 or fewer repetitions. Most of them also did the squat and deadlift; some did not, for medical reasons. Predicted and measured 1RMs correlated highly (r above 0.95), yet the formulas on average came out lower than the weight people actually lifted:

• Bench press: Epley was 2.2 lb (1.0 kg) lower on average (1%), Lombardi 4.3 lb (2.0 kg, 3%) and Brzycki 5.4 lb (2.4 kg, 4%).
• Squat: 6.7 lb (3.0 kg) lower for Epley, 10.7 lb (4.9 kg) for Brzycki and 11.2 lb (5.1 kg) for Lombardi. The paper's text puts the gap at 2 to 8% across all seven formulas it tested.
• Deadlift: 24.0 lb (10.9 kg) lower for Epley (10%), 27.4 lb (12.4 kg) for Lombardi (11%) and 29.1 lb (13.2 kg) for Brzycki (12%).

These are group averages from young people new to lifting. One person's estimate can be further off in either direction. Reynolds and colleagues also found that prediction formulas need to be exercise specific, so an estimate from one exercise does not carry over to another.

The percentage table

The load table works out 40 to 95% of one estimate, rounded to 0.1 kg or lb. By default it uses the lowest of the three estimates. That is a cautious default chosen for this page, not a rule from the studies: a first set that feels too light is easy to fix. You can switch the table to one formula instead. Every load in the table is an estimate of an estimate, so round it to the plates or weights you have, and adjust it by how the set feels.

The ACSM position stand (Garber and colleagues, 2011) gives these loads for apparently healthy adults, with each major muscle group trained 2 to 3 days a week:

For most adults the same position stand recommends 8 to 12 repetitions a set to improve strength and power, and it says 10 to 15 repetitions work for middle aged and older people starting exercise. The weight should let you finish the set with the muscle fatigued but not exhausted. The rows at 80% and above are heavy loads that ACSM gives for experienced strength trainers. If you are starting at 40 to 50%, use the bottom rows of the table, and your physio can set the exact load.

How physios use an estimated 1RM to set rehab loads

Reynolds and colleagues list rehabilitation specialists among the professionals who use the 1RM to prescribe training. For a patient whose age or health makes a maximal lift unsafe, an estimate from a lighter set gives the physio a starting number. The physio then chooses the percentage and the number of repetitions for that person.

Garber and colleagues suggest that older, very deconditioned or frail people can begin at a lower resistance, perhaps 40 to 50% of 1RM, with more repetitions (10 to 20). Once they have an acceptable level of muscle conditioning, the resistance can go up. The formulas are exercise specific. To track progress, retest on the same exercise and equipment, and count repetitions the same way each time. Reynolds and colleagues caution against using their own equations on different equipment or with a different lifting speed or rest time.

Both studies tested healthy people. LeSuer's group used college students. Reynolds and colleagues excluded anyone with a known disease or more than one heart disease risk factor besides age. Neither study shows how well the formulas work for patients. A set to fatigue is still hard work, and your physio decides whether it suits you and how heavy it should be.

The ACSM loads are for apparently healthy adults. After an injury or surgery, the treating physio or surgeon sets the loads and when they can go up.

Safety

Do not test a true one rep max without supervision. A maximal attempt needs someone trained watching you, and on a barbell lift such as the bench press or squat, a spotter. A set to fatigue on those lifts needs a spotter or a rack with safety bars too, because the last repetition can fail with the bar over your chest or on your back. The calculator is there so you can work from a lighter set instead.

With a heart condition or high blood pressure, check with your doctor before you start. If you are pregnant or have had recent surgery, ask your doctor or physio before you lift to fatigue. Breathe out as you lift and in as you lower, as the ACSM position stand advises. Do not hold your breath while you push, especially if you have high blood pressure.

With osteoporosis or a past spinal fracture, do not test a maximal lift, and ask your physio which exercises and loads suit you before you lift to fatigue. The UK consensus statement on exercise for osteoporosis (Brooke-Wavell and colleagues, 2022) advises against bending the spine far forward, especially with a weight. Too Fit to Fracture (Giangregorio and colleagues, 2015) adds twisting with a weight and lifting weights from the floor, so check with your physio before a deadlift from the floor.

Stop and rest if you notice any of these:

• Chest pain or pressure, dizziness or feeling faint, a racing or irregular heartbeat, or being far more out of breath than the effort should cause.
• Sharp pain in a joint, or a joint that gives way.
• Pain, numbness or tingling running down an arm or a leg.
• A sudden, severe headache.

If chest pain, pressure or tightness does not ease quickly when you rest, spreads to your arm, neck, jaw, stomach or back, or comes with sweating, feeling sick, feeling light-headed or being short of breath, call emergency services straight away, as this can be a heart attack. If it eases quickly and none of these happen, get medical advice the same day, and do not exercise again until you have been checked. If you faint while exercising, call emergency services, even if you feel fine again quickly. A sudden, severe headache unlike anything you have had before needs emergency help.

Sources

1. LeSuer DA, McCormick JH, Mayhew JL, Wasserstein RL, Arnold MD. The accuracy of prediction equations for estimating 1-RM performance in the bench press, squat, and deadlift. Journal of Strength and Conditioning Research. 1997;11(4):211-213. doi:10.1519/00124278-199711000-00001
2. Reynolds JM, Gordon TJ, Robergs RA. Prediction of one repetition maximum strength from multiple repetition maximum testing and anthropometry. Journal of Strength and Conditioning Research. 2006;20(3):584-592. doi:10.1519/00124278-200608000-00020
3. Brzycki M. Strength testing: predicting a one-rep max from reps-to-fatigue. Journal of Physical Education, Recreation and Dance. 1993;64(1):88-90. doi:10.1080/07303084.1993.10606684
4. Epley B. Poundage chart. In: Boyd Epley Workout. Lincoln, NE: Body Enterprises; 1985. Cited by LeSuer and colleagues and by Reynolds and colleagues.
5. Lombardi VP. Beginning Weight Training. Dubuque, IA: W.C. Brown; 1989. Cited by LeSuer and colleagues and by Reynolds and colleagues.
6. Garber CE, Blissmer B, Deschenes MR, et al. American College of Sports Medicine position stand. Quantity and quality of exercise for developing and maintaining cardiorespiratory, musculoskeletal, and neuromotor fitness in apparently healthy adults: guidance for prescribing exercise. Medicine and Science in Sports and Exercise. 2011;43(7):1334-1359. doi:10.1249/MSS.0b013e318213fefb
7. Brooke-Wavell K, Skelton DA, Barker KL, et al. Strong, steady and straight: UK consensus statement on physical activity and exercise for osteoporosis. British Journal of Sports Medicine. 2022;56(15):837-846. doi:10.1136/bjsports-2021-104634
8. Giangregorio LM, McGill S, Wark JD, et al. Too Fit To Fracture: outcomes of a Delphi consensus process on physical activity and exercise recommendations for adults with osteoporosis with or without vertebral fractures. Osteoporosis International. 2015;26(3):891-910. doi:10.1007/s00198-014-2881-4

This calculator gives general estimates for education. It is not a medical assessment or a personal training plan.