One Rep Max Calculator (1RM) and % Chart

How the 1RM is estimated

Your headline number is the average of the two most widely used equations, where w is the weight lifted and r the reps completed:

Epley: 1RM = w × (1 + r ÷ 30) Brzycki: 1RM = w × 36 ÷ (37 − r)

Epley's equation comes from his 1985 coaching charts at the University of Nebraska¹; Brzycki published his in 1993.² The two agree closely around 10 reps; below that, Epley reads slightly higher. The calculator also shows four other published equations for comparison:

Formula	Equation
Epley	`w × (1 + r / 30)`
Brzycki	`w × 36 / (37 − r)`
Lander	`100w / (101.3 − 2.67123r)`
Lombardi	`w × r^0.10`
Mayhew	`100w / (52.2 + 41.9e^(−0.055r))`
Wathan	`100w / (48.8 + 53.8e^(−0.075r))`

Accuracy drops as reps rise and differs between lifts, so estimates from more than 10 reps are flagged.³

Adding reps in reserve (RPE)

Reps used = reps completed + (10 − RPE)

The repetitions-in-reserve RPE scale validated by Zourdos and colleagues lets a set stopped short of failure count as the set it would have been.⁴ Five reps at RPE 8 are treated as seven reps to failure.

Worked example

225 lb for 5 reps on the bench press:

Epley: 225 × (1 + 5 ÷ 30) = 262.5 lb Brzycki: 225 × 36 ÷ 32 = 253.1 lb Estimated 1RM: (262.5 + 253.1) ÷ 2 = 257.8 lb, about 260 lb

% of 1RM	Load	Max reps
100%	260 lb	1
95%	245 lb	2
90%	230 lb	3
85%	220 lb	5
80%	205 lb	8
75%	195 lb	10
70%	180 lb	13

Loads are rounded to the nearest 5 lb or 2.5 kg so you can load them with standard plates.

Using percentages to plan training

Strength work usually sits at 80 to 90% for sets of 2 to 5, leaving one or two reps in reserve.
Muscle-building work works across a wide range; 65 to 80% for sets of 6 to 12 is common and easy to recover from.
The ACSM recommends progressing load by about 2 to 10% once you can exceed your target reps for one or two sessions.⁵

Strength and body composition go together: see the protein calculator for the intake that supports muscle gain, and the exercise library for technique on every lift.

Frequently asked questions

Which one-rep max formula is most accurate?

No single formula wins for every lift and person. In a comparison on the bench press, squat and deadlift, the Mayhew and Wathan equations were closest for the bench press, and all equations became less accurate for the squat and deadlift and as reps increased. Averaging Epley and Brzycki, as this calculator does, gives a sensible middle estimate from sets of 10 reps or fewer.

Is it safe to test a true one-rep max?

For experienced lifters with good technique, a spotter or safety bars, and a proper warm-up, a max attempt is reasonably safe. For beginners, estimating from a hard set of 3 to 5 reps gives most of the information with much less risk and fatigue.

How often should I retest my 1RM?

Every 4 to 8 weeks, at the end of a training block, is enough for most people. You can re-estimate more often from your normal working sets: if a set that used to be hard now moves quickly, your max has gone up.

What does RPE mean in the calculator?

RPE (rating of perceived exertion) on the 1 to 10 lifting scale tells the calculator how many reps you had left. RPE 10 means you could not have done another rep; RPE 8 means about two more. Those reps in reserve are added before estimating, so a set you stopped early still gives an accurate max.

Why do the formulas disagree at high reps?

Endurance varies a lot between people and lifts, so the relationship between reps and max load is less predictable the further you get from a single. Estimates from 2 to 6 reps are the most consistent; above about 10 reps the spread between formulas grows quickly.

One Rep Max (1RM) Calculator

How the 1RM is estimated

Adding reps in reserve (RPE)

Worked example

Using percentages to plan training

Frequently asked questions

Sources

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