One Rep Max Calculator

About the One Rep Max Calculator

Your one rep max (1RM) is the heaviest weight you can lift once with good form. It is the standard measure of strength in the squat, bench press and deadlift, and most strength programmes prescribe their weights as a percentage of it. Testing a true max, though, is tiring, needs a spotter and carries a higher risk of injury — so most lifters estimate it from a heavier set of several reps instead.

This one rep max calculator estimates your 1RM from the weight and number of reps in any set, using seven published formulas: Epley, Brzycki, Lombardi, O'Conner, Mayhew, Wathan and Lander. It shows your chosen formula as the headline, all seven side by side, their average and range, and a chart of training loads from 60 to 95 percent of your estimated max.

How to Use the One Rep Max Calculator

Enter the weight lifted and choose kg or lb.

Enter the number of reps completed — ideally a hard set of 10 reps or fewer, taken close to failure.

Choose the formula for the headline; Epley is the default.

The Formulas

  Epley      1RM = w × (1 + r ÷ 30)
  Brzycki    1RM = w × 36 ÷ (37 − r)
  Lombardi   1RM = w × r^0.10
  O'Conner   1RM = w × (1 + 0.025 × r)
  Mayhew     1RM = 100 × w ÷ (52.2 + 41.9 × e^(−0.055 × r))
  Wathan     1RM = 100 × w ÷ (48.8 + 53.8 × e^(−0.075 × r))
  Lander     1RM = 100 × w ÷ (101.3 − 2.67123 × r)

  w = weight lifted, r = reps completed

A single rep is already a one rep max, so for one rep every formula returns the weight itself.

Step-by-Step Example

A lifter bench presses 100 kg for 5 reps.

  Epley      100 × (1 + 5 ÷ 30)   = 116.7 kg
  Brzycki    100 × 36 ÷ (37 − 5)  = 112.5 kg
  Lombardi   100 × 5^0.10         = 117.5 kg
  O'Conner   100 × (1 + 0.125)    = 112.5 kg
  Mayhew                          = 119.0 kg
  Wathan                          = 116.6 kg
  Lander                          = 113.7 kg

  average of the seven            = 115.5 kg

The estimates range from 112.5 to 119 kg. A training max of around 115 kg is a sensible working figure; the only way to know exactly is to test it.

Percentages of One Rep Max

With an Epley estimate of 116.7 kg:

  95%   110.8 kg        75%   87.5 kg
  90%   105.0 kg        70%   81.7 kg
  85%    99.2 kg        65%   75.8 kg
  80%    93.3 kg        60%   70.0 kg

As a rough guide, most lifters can manage about 2 reps at 95 percent, 4 at 90, 6 at 85, 8 at 80 and 10 at 75 percent, although this varies from person to person and between lifts.

Which Formula Should You Use?

Research comparing the formulas has not found one that is best for everyone. Epley and Brzycki are the most widely used, and they give identical answers at exactly 10 reps: 80 kg for 10 gives 106.7 kg with both. Below 10 reps Brzycki estimates lower than Epley, and above 10 it estimates higher. The Lombardi and O'Conner formulas tend to give lower estimates from high-rep sets. Taking the average of several formulas smooths out their individual biases, which is why the calculator shows it alongside your chosen formula.

Why Low-Rep Sets Are More Accurate

Every formula assumes a fixed relationship between strength and endurance, and that relationship varies a great deal between people. Some lifters can do 15 reps at 70 percent, others only 8. The further the set is from a single rep, the more that individual difference affects the estimate. With 60 kg for 12 reps, the seven formulas already spread from 76.9 to 86.6 kg — nearly 10 kg. A hard set of 3 to 6 reps gives a much tighter and more trustworthy estimate.

Testing a True One Rep Max

Powerlifters and strength athletes test their true max before competitions or at the end of a training block. To test safely, warm up thoroughly, work up in progressively heavier singles, rest several minutes between attempts, use a spotter or safety bars, and stop when form breaks down. For most people who train for fitness or muscle, an estimated max is accurate enough to set training weights, with far less risk and fatigue.

Using Your Estimate in Training

Most strength programmes are written in percentages of a one rep max, so a good estimate is what turns a plan on paper into weights on the bar. Heavy strength work usually sits between 80 and 90 percent of your max for sets of 3 to 6 reps. Muscle-building work is often done at 65 to 80 percent for sets of 8 to 12, and technique or recovery sessions use lighter loads again. Because the estimate comes from your recent training, it moves with you: re-enter a fresh hard set every few weeks and your percentages stay current without the fatigue of testing. Round the loads to the plates you have, and if a prescribed set feels far too easy or impossibly hard, trust the bar over the formula and adjust the estimate.

Tracking Progress Over Time

An estimated max is also a simple way to see whether you are getting stronger. Lifting 100 kg for 5 one month and 100 kg for 7 the next is real progress, but it is hard to compare with a heavier set of 3. Converting each into an estimated one rep max puts them on the same scale: 116.7 kg, then about 123.3 kg by Epley. Use the same formula each time so the numbers stay comparable, and look at the trend over several weeks rather than any single session.

Understanding Your Result

The headline is your estimated one rep max using the chosen formula.

The all seven formulas line shows every estimate side by side.

The average line gives the mean of the seven and their range.

The training loads line gives 95 down to 60 percent of the headline estimate.

When Should You Use This Calculator?

Use it to estimate your max without testing it.

Use it to set working weights for a programme written in percentages.

Use it to track strength progress from your normal training sets.

Use it to compare lifts or lifters on a common scale.

Common Mistakes

Using a set that was not close to failure. An easy set underestimates your max.

Using very high reps. Above 10 reps the estimates spread widely.

Treating the estimate as exact. Expect a few percent either way.

Mixing lifts. Estimate each lift separately; a squat set says nothing about your bench.