How do I calculate my one-rep max?

Take a set to near failure at a weight you can lift for two to six reps, then apply a formula. The Epley equation — weight × (1 + reps ÷ 30) — is the most common. This calculator applies four published formulas and averages them, which is more reliable than trusting any single one.

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

For experienced lifters with solid technique and a spotter, yes. For beginners it is generally unnecessary — an estimate from a set of five gives you everything you need for programming without the technique breakdown that maximal attempts invite. Most people never need to test a true max.

How often should I re-test my 1RM?

Every six to twelve weeks is plenty. Rather than a true max attempt, take a heavy set of three to five reps close to failure and re-estimate. That gives you a current number with far less fatigue and risk.

Why do the four formulas give different numbers?

Each was fitted to a different dataset and uses a different curve. At low reps they agree closely. As reps rise, the relationship between reps and maximum force becomes less predictable and more individual, so the curves diverge. The spread between them is itself useful information about how much to trust the estimate.

Does 1RM differ between exercises?

Yes, considerably. The formulas tend to work best on big compound barbell lifts. On isolation exercises and on movements with a large stability component, rep performance at a given percentage varies much more, so treat estimates there with more caution.

Strength

One-rep max calculator

Enter the weight you lifted and how many reps you got, and this estimates your one-rep max using four published formulas — Epley, Brzycki, Lombardi and Lander — rather than one. It also gives you the full percentage table for programming, and shows where your lift sits against general strength standards.

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How this is calculated

Epley

1RM = w × (1 + r ÷ 30)

The most widely used formula. Tends to give slightly higher estimates than Brzycki above five reps.

Brzycki

1RM = w × 36 ÷ (37 − r)

Very close to Epley at low reps and diverges below it as reps rise. Breaks down entirely at 37 reps, which tells you something about its intended range.

Lombardi

1RM = w × r^0.10

A power-law fit. Tends to read conservatively at higher rep counts.

Lander

1RM = (100 × w) ÷ (101.3 − 2.67123 × r)

Similar in shape to Brzycki. Included because averaging several formulas is more robust than trusting any single one.

What your result means

Reps performed	Estimate reliability	What to do with it
1–3	High	Close to a true max. Safe to programme directly from.
4–6	Good	The sweet spot for estimating. Most formulas agree closely here.
7–10	Moderate	Usable, but treat the number as a range rather than a figure.
11+	Low	Endurance and technique start dominating. Re-test with a heavier set.

All four formulas were fitted to relatively low-rep sets, which is why they diverge as reps climb.

How accurate is a 1RM calculator?

Reasonably accurate from sets of about two to six reps, and progressively less so beyond that. Below six reps the four formulas typically agree within a few percent. By ten reps they can differ by more than five percent, because a high-rep set is limited as much by muscular endurance and technique as by maximum force.

There is also individual variation the formulas cannot capture. Some people can grind out many reps at a high percentage of their max; others are far more limited past a few. If you consistently get more reps at a given percentage than the table predicts, adjust your own numbers accordingly rather than trusting the formula.

Why use four formulas instead of one?

Because they disagree, and showing the spread is more honest than picking one and presenting it as fact. Each formula is a curve fitted to a particular dataset, and none of them is universally correct. Averaging them gives a more robust central estimate, and seeing the range tells you how much confidence the number deserves.

When the four estimates cluster tightly, your set was in the range these formulas handle well. When they fan out, it is a signal to test with a heavier, lower-rep set before basing a training block on the number.

How to use the percentage table

Most strength programmes prescribe load as a percentage of your one-rep max. The table under your result converts your estimate into working weights, with the rep count typically associated with each percentage. Use it as a starting point and adjust based on how the first working set actually feels.

One caution: percentages assume your max is current. Strength changes, and an estimate from three months ago will mislead you in both directions. Re-testing every six to twelve weeks with a heavy set of three to five keeps the number honest without the risk of a genuine max attempt.

What counts as a good lift?

That depends heavily on your bodyweight, sex, age, limb proportions and how long you have trained. The strength-level bands here are a rough orientation compiled from commonly published charts — useful for a general sense of where you sit, not a precise ranking.

For real data rather than guide bands, OpenPowerlifting publishes its complete competition database in the public domain. It is the best free source for what actual lifters at a given bodyweight are lifting, though it is skewed toward people who compete.

Frequently asked questions

How do I calculate my one-rep max?: Take a set to near failure at a weight you can lift for two to six reps, then apply a formula. The Epley equation — weight × (1 + reps ÷ 30) — is the most common. This calculator applies four published formulas and averages them, which is more reliable than trusting any single one.
Is it safe to test a true one-rep max?: For experienced lifters with solid technique and a spotter, yes. For beginners it is generally unnecessary — an estimate from a set of five gives you everything you need for programming without the technique breakdown that maximal attempts invite. Most people never need to test a true max.
How often should I re-test my 1RM?: Every six to twelve weeks is plenty. Rather than a true max attempt, take a heavy set of three to five reps close to failure and re-estimate. That gives you a current number with far less fatigue and risk.
Why do the four formulas give different numbers?: Each was fitted to a different dataset and uses a different curve. At low reps they agree closely. As reps rise, the relationship between reps and maximum force becomes less predictable and more individual, so the curves diverge. The spread between them is itself useful information about how much to trust the estimate.
Does 1RM differ between exercises?: Yes, considerably. The formulas tend to work best on big compound barbell lifts. On isolation exercises and on movements with a large stability component, rep performance at a given percentage varies much more, so treat estimates there with more caution.

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Sources

This tool provides general information about exercise and nutrition. It is not medical advice and not a substitute for a qualified professional. If you have a health condition, are pregnant, or are recovering from injury, speak to a doctor or registered dietitian before acting on any of these numbers.