One Rep Max Calculator

Estimate your 1RM from any set

One Rep Max Calculator

One Rep Max for

lifted for

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One Rep Max (1RM): How the Estimate Works and How to Use It

What is a one rep max?

Your one rep max — written 1RM — is the heaviest weight you could lift for a single clean repetition of an exercise. It is the reference point almost every strength programme is written against: sets are prescribed as a percentage of it rather than as an absolute weight, so the same programme scales to any lifter.

Testing a true single is slow and carries real injury risk, so the number is normally estimated from a set you have already done. That is what this one rep max calculator does: enter the weight you lifted and how many reps you got, and it works backwards to the single you never had to attempt.

The formula

The answer above uses the Epley formula:

1RM = weight × (1 + reps ÷ 30)

It treats each additional repetition as worth about 3.33% more weight. Six other published formulas — Brzycki, Lombardi, O'Conner, Wathan, Lander and Mayhew — are shown on every result page so you can see how much they disagree for your particular set.

How many reps should you use?

  • 2–6 reps: the accurate zone. All the formulas cluster tightly here.
  • 7–12 reps: usable, but the estimate starts to depend on which formula you pick.
  • 13+ reps: you are measuring muscular endurance more than maximal strength — treat any number as a rough guide.

Whichever set you use, it should have been taken close to failure. A comfortable set of five understates your max exactly as much as it was easy.

Turning a 1RM into training weights

Once you have the number, load is usually prescribed as a percentage of it: roughly 85–95% for heavy strength work, 75–85% for the main working sets of most programmes, and 65–75% for volume, technique and speed work. Every result page prints that percentage table for your own max.

Pounds or kilograms?

Both. Every 1RM formula is a ratio, so the estimate comes out in whatever unit you entered — pick pounds or kilograms and the answer, the rep table and the training percentages all follow.

Common one rep max examples

Note: an estimated 1RM is a planning tool, not a target to chase. Warm up properly, keep your technique, and use a spotter before attempting a genuine maximal single.

See Also

One Rep Max Calculator

This calculator estimates your one-rep max (1RM) — the heaviest weight you could lift for a single repetition — from a set you have already completed. For example, it can help you find out what is the one rep max for 225 lbs × 5 reps? (The answer is: 262.5 lbs). Enter the weight you lifted (e.g. 225), pick pounds or kilograms, and enter how many reps you managed (e.g. 5).

FAQ

What is a one rep max?

Your one rep max (1RM) is the heaviest weight you can lift for a single repetition of an exercise with good form. Because testing it directly is risky, it is normally estimated from a lighter set taken close to failure.

Which formula does this calculator use?

The answer uses the Epley formula: 1RM = weight × (1 + reps ÷ 30). Six other published formulas — Brzycki, Lombardi, O'Conner, Wathan, Lander and Mayhew — are shown alongside it for comparison.

How accurate is an estimated 1RM?

Estimates are most reliable at 2 to 6 reps and drift further from reality as the rep count grows, because endurance starts to matter more than maximal strength. Above 12 reps treat any estimate as a rough guide only.

Does it work with kilograms as well as pounds?

Yes. Every 1RM formula is a ratio, so the estimate comes out in the same unit you entered. Pick pounds or kilograms and the answer, the rep table and the training percentages all follow that unit.