One Rep Max Calculator

Use our free one rep max calculator to estimate your 1RM from any set, without testing a true max. It runs six formulas, averages them, and gives you your full training percentage chart.

One Rep Max Calculator

Weight lifted (kg) Reps completed

What Is One Rep Max?

Your one rep max, or 1RM, is the heaviest weight you can lift once with proper form. It is the gold standard for absolute strength, and nearly every serious training program prescribes work as a percentage of it. Testing a true max is risky and fatiguing, so this calculator estimates your 1RM from a submaximal set taken close to failure.

This one rep max calculator gives you that estimate without a risky max attempt.

How This One Rep Max Calculator Works

Enter the weight you lifted and the reps you completed, and the calculator runs six proven formulas and averages them. Each formula makes different assumptions, so showing all six plus the average hedges against any single model being biased for your rep range.

Every one rep max calculator result includes the spread between the highest and lowest formula, so you can see how much to trust the number.

Formula	Equation	Best for
Epley	w x (1 + r/30)	Best for 2-10 reps
Brzycki	w x 36/(37 – r)	1-10 reps, conservative
Lombardi	w x r^0.10	Low reps
O’Conner	w x (1 + r/40)	Simple, conservative
Wathan	100w/(48.8 + 53.8 x e^-0.075r)	Wide rep range
Mayhew	100w/(52.2 + 41.9 x e^-0.055r)	Higher reps, bench press

Research found 5-rep sets predict 1RM most accurately, and no more than 10 reps should be used in linear 1RM equations. In the formulas, w is the weight lifted and r is the reps completed. The spread between the highest and lowest formula result is shown with your result. A tight spread means the estimate is trustworthy, while a wide spread means the set was too far from failure or too high in reps.

Worked Example

Say you squat 100 kg for 5 reps. The six formulas give Epley 116.7, Brzycki 112.5, Lombardi 117.5, O’Conner 112.5, Wathan 116.6, and Mayhew 119.0, for an average 1RM of 115.8 kg with a spread of 6.5 kg. Your training weights then follow from that average: 90% is 104.2 kg for strength work, 80% is 92.6 kg for hypertrophy, and 70% is 81.1 kg for muscle endurance.

Enter your own numbers in the one rep max calculator above to get your training weights.

Common One Rep Max Calculator Problems (And How to Fix Them)

The calculator says I can lift it but I failed: estimates assume a near-failure set with good form. If you left 2-3 reps in the tank, the estimate overshoots. Retest with a true near-failure set.
I used 15 reps and the number looks absurd: the formulas break down past 10 reps. Retest with a heavier weight for 3-8 reps.
The formulas disagree by a lot: the spread warning is doing its job. Use the average as your working number and program conservatively until a retest tightens it.
My estimated 1RM is lower than last month: fatigue, poor sleep, and bad days lower performance. One estimate is a snapshot. Retest fresh after a rest day.
Should I attempt my estimated 1RM: not without a spotter, a proper warm-up, and a plan. The estimate is for programming percentages, not a dare. True max attempts belong in peak week.

If your one rep max calculator numbers look off, retest with a heavier weight for 3-8 reps.

How to Use Your 1RM

Program off percentages: 85-90% for strength (3-5 reps), 70-80% for hypertrophy (6-12 reps), and 90-97% for peaking singles and doubles. Retest every 4-8 weeks, and support your training with our protein intake calculator and calorie calculator.

Bookmark this one rep max calculator and retest every 4-8 weeks to keep your percentages current.

Frequently Asked Questions

What is one rep max?

The heaviest weight you can lift once with proper form. It is the standard measure of absolute strength and the base for most training programs.

How is 1RM calculated without testing a max?

From a set taken close to failure. This calculator runs six formulas on your weight and reps and averages them for a balanced estimate.

Which 1RM formula is most accurate?

It depends on rep range. Brzycki and Epley are best for 2-10 reps. Mayhew and Wathan handle higher reps better. The average of all six is the most robust single number.

How many reps should I use for the most accurate estimate?

3-8 reps to near failure. Research found 5-rep sets predict 1RM most accurately, and estimates get unreliable past 10 reps.

Is it safe to test my true 1RM?

It carries risk without a spotter, proper warm-up, and a plan. For most lifters, estimating from a submaximal set is safer and accurate enough for programming.

Why do the formulas disagree?

Each was fitted to different lifters and rep ranges. The spread between them tells you how much to trust the estimate: tight spread means trustworthy, wide spread means retest.

How often should I retest my 1RM?

Every 4-8 weeks, or after finishing a training block. Update your training percentages from the new number.

What percentage of 1RM builds muscle?

70-80% for hypertrophy (6-12 reps). 85-90% for strength (3-5 reps). 90-97% for peaking singles and doubles.

Does 1RM work for all exercises?

The formulas work for any lift, but they were validated mostly on barbell lifts like squat, bench, and deadlift. Machine and isolation lifts vary more.

One Rep Max Calculator