// Strength Calculators

1RM Calculator

Enter a set you have genuinely completed — the weight and the reps — to estimate your one-rep max and your working percentages.

Your details

Your result

Estimated lift 1RM
91.7kg
Working weight for 5 reps
80kg
90% (3 reps)
82.5kg
80% (8 reps)
73.3kg
70% (12 reps)
64.2kg
  • Averaged from the Epley and Brzycki formulas. Most accurate at 1–8 reps.

Estimates are for general guidance only and are not medical advice. For a personalised plan, book a free guided tour at RPM Gym.

What your result means

The headline number is an estimated one-rep max: the load you would be predicted to lift once, based on a set you did for more than one rep. It's an estimate from a rep-max relationship, not a tested maximum.

The percentages below it are what the number is actually for. Most strength programmes are written as percentages of 1RM, so an estimate lets you programme without repeatedly testing a true max — which is the fatiguing and higher-risk part of training.

How it is calculated

Epley and Brzycki rep-max equations, averaged

Epley: 1RM = weight × (1 + reps ÷ 30). Brzycki: 1RM = weight × 36 ÷ (37 − reps). This tool reports the mean of the two.

What it assumes

  • The set was taken close to failure. A set with several reps left in reserve produces an underestimate, because the equations assume the rep count was near-maximal.
  • Both equations were derived from group data and diverge as reps rise. Epley reads higher, Brzycki lower, and averaging them keeps the estimate between the two.
  • Technique is consistent between the set you entered and a true single. A grinding rep with form breakdown isn't the same input as a clean one.

Units and rounding

  • Weight is entered in kilograms; the estimate and every percentage return in kilograms.
  • Reps are whole numbers. At one rep, both equations return the weight entered.
  • Brzycki divides by (37 − reps), which breaks down at 37 reps and beyond, so the implementation returns no result there rather than a negative or infinite load.

Worked example

A set of 5 reps at 100 kg, taken close to failure.

  1. Epley: 100 × (1 + 5 ÷ 30) = 100 × 1.1667 = 116.7 kg
  2. Brzycki: 100 × 36 ÷ (37 − 5) = 100 × 36 ÷ 32 = 112.5 kg
  3. Average: (116.7 + 112.5) ÷ 2 = 114.6 kg
  4. 90% = 103.1 kg · 80% = 91.7 kg · 70% = 80.2 kg

An estimated 1RM of about 114.6 kg, with working sets around 103 kg for triples and 92 kg for eights.

Limitations

  • Accuracy falls as reps rise. The equations are most reliable at one to eight reps; a set of fifteen produces a number with wide error bars in either direction.
  • The estimate is lift-specific and doesn't transfer. A squat estimate says nothing about your bench, and higher-rep-tolerant lifts like the leg press tend to read high.
  • Rep quality isn't an input. Two lifters can move the same weight for the same reps with very different proximity to failure and get an identical, misleading estimate.
  • An estimate isn't a licence to attempt the number. Testing a true max needs a warm-up progression, a safe setup and ideally a spotter.
  • If you have an injury, pain during the lift, or you're returning after a break, the estimate isn't the input that matters. How the lift feels is.

What to do next

  • Programme from percentages rather than the max itself. Most work sits between 70% and 85% for hypertrophy and 85%+ for low-rep strength work.
  • Re-estimate from a real set every four to six weeks instead of retesting a true single. It costs one working set instead of a session.
  • Enter your best recent set per lift separately. A single 'strength number' across all lifts will misrepresent at least one of them.
  • If the percentages feel consistently wrong in the gym, trust the gym. Adjust the working weight and re-estimate from the set that actually happened.

Sources

Related calculators
RPEPlateDeadlift 1RMTraining VolumeWilks ScoreBench Press 1RM
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// Frequently Asked

Questions, answered.

How accurate is a 1RM calculator?

Reasonably accurate from low-rep sets taken close to failure — typically within a few percent at one to five reps. Error grows with rep count, so a set of ten gives a rougher estimate and a set of twenty is barely informative.

Why do Epley and Brzycki give different answers?

They are different curve fits to different datasets. Epley scales linearly with reps and reads higher as reps climb; Brzycki uses a divisor that pulls the estimate down. Averaging them avoids inheriting either equation's bias.

How many reps should I use for the most accurate estimate?

Three to five, taken close to failure. That range is high enough to be safer than a true single and low enough that both equations are still in the part of their range where they agree.

Should I test my actual one-rep max?

Only if you need the number for a reason: a competition, or a programme that requires a tested max. For ordinary training, estimating from a working set gives you what you need without the fatigue cost or the risk of a maximal single.

Does this work for every exercise?

It works best on compound barbell lifts with a stable groove: squat, bench, deadlift, overhead press. Machine and isolation movements tolerate higher reps differently, so estimates from them tend to run high.

My estimate went down. Did I lose strength?

Not necessarily. The estimate is only as good as the set you entered — a set further from failure, taken when tired, or done after heavy accessory work will estimate lower without any strength being lost.

Know the number. Now use it properly.

RPM Gym's strength floor in Al Manhal is set up for percentage-based work, and the coaching team can check your lift before you push the top end. Book a free guided tour.

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