One Rep Max Calculator
Estimate your one-rep max from a set at any weight, using five published formulas, plus a full percentage training table.
How to use this calculator
- 1Perform a set to within a rep or two of failure with good form.
- 2Enter the weight and the number of clean reps.
- 3Use sets of 3–5 reps for the most reliable estimate.
- 4Read training loads off the percentage table rather than testing your true max.
How the calculation works
Epley: 1RM = w × (1 + r/30)
Brzycki: 1RM = w × 36 / (37 − r)
Lombardi: 1RM = w × r^0.10- w
- Weight lifted
- r
- Repetitions completed to near-failure
All are empirical fits to observed strength data. They agree within 1–2% at 3–5 reps and diverge substantially beyond 10.
Brzycki becomes undefined at 37 repetitions, where its denominator reaches zero — a clear signal these formulas are not meant for high-rep sets.
The average of several estimators is more robust than any single one, which is why it is the headline figure here.
Worked example
5 reps at 100 kg
- 1.Epley: 100 × (1 + 5/30) = 116.7 kg.
- 2.Brzycki: 100 × 36 ÷ (37 − 5) = 112.5 kg.
- 3.Lombardi: 100 × 5^0.1 = 117.5 kg.
- 4.Averaging all five gives about 115 kg — and the tight spread reflects that 5 reps is in the reliable range.
Result: About 115 kg
What a one-rep max represents
A one-rep max (1RM) is the heaviest load someone can lift for exactly one complete repetition with acceptable form. It functions as a personal benchmark in strength training — a single number that programming, competition standards and progress tracking can all be built around, in the same way a runner’s personal best time anchors their training paces.
Why estimate it instead of testing it directly
Testing a true 1RM safely requires a proper warm-up progression, a spotter for barbell lifts, and enough technical experience with the movement that fatigue does not compromise form under near-maximal load — conditions not everyone training alone has access to, and even under ideal conditions, true max testing is fatiguing enough that it disrupts training for days afterward. Estimating from a submaximal set taken close to failure gives programming-quality information without that cost, which is why prediction formulas have been in continuous use in strength sport since at least the 1980s.
Training by percentage of 1RM
Once a 1RM is known or estimated, most structured strength programmes prescribe working weights as a percentage of it rather than as an absolute number, because percentages scale automatically as the lifter gets stronger. Different percentage ranges are conventionally associated with different training effects.
- Near-maximal loads (roughly 85% and above) — trained for a small number of reps, generally associated with the greatest gains in maximal strength and neural efficiency.
- Moderate loads (roughly the mid-60s to mid-80s percent) — the range classically associated with muscle growth, trained for moderate rep counts.
- Lighter loads (below roughly 65%) — trained for higher reps, more associated with muscular endurance than with maximal strength or size.
Why the formulas disagree more as reps increase
Every 1RM formula is an empirical curve fit to observed strength data, not a law of physics, and each was built from a different set of lifters performing a different mix of exercises. At low rep counts — three to five — the formulas cluster tightly because there is little room for fatigue or pacing differences to distort the result. As rep count rises, muscular endurance and individual fatigue resistance increasingly determine how many reps someone can complete at a given weight, which is precisely the variability these formulas cannot account for, and why their predictions spread further apart the higher the rep count used to generate them.
What this assumes, and where it stops
Assumptions
- The set was taken close to muscular failure with consistent form.
- The lift is a standard compound movement. These formulas were derived largely from bench press and squat data.
Limitations
- Accuracy falls sharply above 8–10 repetitions, where muscular endurance rather than maximal strength dominates.
- Isolation exercises and machines behave differently from the compound lifts these formulas were fitted to.
- Individual variation is large — some lifters consistently over- or under-perform their predicted max.
Common questions
How accurate is a one-rep max estimate?
Within roughly 2–5% when calculated from a set of 3–5 reps, which is good enough for programming. Beyond 10 reps, error can exceed 10% because you are increasingly measuring endurance rather than maximal strength.
Should I just test my actual one-rep max?
Rarely. True max testing carries real injury risk, requires a spotter and full warm-up, and leaves you fatigued for days. For programme design an estimate from a 3–5 rep set is accurate enough and far safer — which is exactly why these formulas exist.
Formula and content last reviewed on .
Results are estimates for information only, not professional advice.
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