What your one rep max means

Your one rep max (1RM) is the heaviest weight you can lift for a single clean repetition of an exercise. Testing it directly is hard on your joints and needs a spotter, so most lifters estimate it from a lighter set of several reps. These prediction equations turn "weight × reps" into a 1RM:

Epley: 1RM = Weight × (1 + Reps ÷ 30)

Brzycki: 1RM = Weight × 36 ÷ (37 − Reps)

Lander: 1RM = 100 × Weight ÷ (101.3 − 2.67123 × Reps)

Lombardi: 1RM = Weight × Reps^0.10

O'Conner: 1RM = Weight × (1 + 0.025 × Reps)

Mayhew and Wathen use an exponential curve: 1RM = 100 × Weight ÷ (a + b × e^(−c × Reps)), with fitted values for a, b and c.

Worked example

Say you bench press 100 kg for 5 reps.

Epley: 100 × (1 + 5 ÷ 30) = 116.7 kg
Brzycki: 100 × 36 ÷ (37 − 5) = 112.5 kg
Average of all seven formulas: about 115.5 kg

The formulas agree within a few kilograms for sets of 10 reps or fewer, which is why this calculator also shows the range. Epley tends to read a little higher on high-rep sets, and Brzycki a little lower.

Percentage of 1RM

Once you know your one rep max, training loads are set as a share of it. Heavier percentages mean fewer reps:

90% and above: 1 to 4 reps, for maximal strength
80% to 85%: 5 to 8 reps, for strength and size
70% to 75%: 10 to 12 reps, for muscle growth
60% to 65%: 15 to 20 reps, for muscular endurance

The chart in the results applies these percentages to your own estimate, so you can see the bar weight for each type of set.

How to use the one rep max calculator

Pick your unit. Choose pounds or kilograms. If you switch after typing, the weight is converted for you.
Enter the weight lifted. Use the total on the bar, including the bar, for a hard set you finished with good form.
Enter the reps. Count only clean reps. Sets of 1 to 10 reps give the most dependable result.
Read your 1RM. The headline number is the average of seven formulas. Open the advanced options to use a single formula such as Epley or Brzycki instead.
Use the chart. The percentage table shows what to load for strength, size and endurance sets.

A few tips for a better estimate: test after a warm-up, rest well between sets, and use the same exercise technique each time. The result applies to the exercise you entered, so work out the bench press, squat and deadlift separately.

Estimates are a planning tool, not a promise. Stop a set before form breaks down, and ask a coach or doctor for advice if you are new to lifting or have an injury.

Frequently Asked Questions

What is a one rep max?

Your one rep max (1RM) is the most weight you can lift for one full repetition of an exercise with good form. It is the standard way to measure maximal strength and to set training loads as percentages.

How do I calculate my one rep max without testing it?

Lift a weight you can handle for several reps, such as 5, then enter the weight and the number of reps. The calculator applies established equations like Epley and Brzycki. For example, 100 kg for 5 reps gives an estimated 1RM of about 112 to 117 kg depending on the formula.

Which one rep max formula is the most accurate?

No single formula is best for everyone. Brzycki and Epley are the most popular, and they agree closely for sets of 10 reps or fewer. Averaging several formulas, as this calculator does by default, reduces the error of any one equation.

How many reps should I use to estimate my 1RM?

Use a hard set of 3 to 8 reps. Accuracy drops as the reps rise, and sets above 10 mostly reflect muscular endurance, so the estimate becomes a rough guide rather than a precise figure.

Is it safe to test a true one rep max?

It can be, with a proper warm-up, a spotter or safety bars, and good technique. Many lifters prefer an estimated 1RM from a lighter set because it carries less risk of injury and less fatigue, especially on the squat and deadlift.

What percentage of my 1RM should I train at?

It depends on the goal. Around 85% to 95% builds maximal strength in low reps, 70% to 80% suits muscle growth in the 6 to 12 rep range, and 60% to 65% works for endurance sets of 15 reps or more. The percentage chart in the results shows the weights for your own max.

Does the calculator work for the bench press, squat and deadlift?

Yes. The equations were developed from multiple exercises, so they work for any lift where you can count clean reps. They tend to be most reliable on the bench press and squat, and slightly less so on the deadlift or Olympic lifts, where technique and grip affect a set.

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