One Rep Max Calculator five equations, one range
Enter a set you actually completed. You get the predicted maximum, the working loads it implies, and what all five published equations say about the same set.
A Prediction, Not a Test
The number comes from a submaximal set. It is an estimate, and it should be treated as one.
Reliable Up to About Ten Reps
Past that the equations diverge sharply and measure endurance more than maximal strength.
What is a one-rep max?
At a Glance
Your one-rep max — 1RM — is the heaviest load you could move for a single clean repetition of a lift. Rather than testing it, which is fatiguing and carries some risk, these equations predict it from a set you have already done, and every training percentage in a programme is then read off that number.
Every one of these equations is a curve fitted to how load and repetitions trade off, published between 1985 and 1993 and still in use. They agree closely at low repetitions and drift apart as the set gets longer.
1RM = w × (1 + r ÷ 30)1RM = w × 36 ÷ (37 − r)The other three follow the same shape: Lombardi multiplies by r raised to 0.10, O'Conner adds 2.5 % per repetition, and Lander divides by a linear term. According to the comparative literature in the Journal of Strength and Conditioning Research, no single equation is best across all lifts and all populations — which is exactly why this page shows all five rather than hiding four of them.
The working loads underneath come from inverting Epley, so the training table can never disagree with the estimate above it.
These are the values the calculator loads by default.
Record the set honestly
100 kg × 5 clean repetitions, taken close to failure. Repetitions left in reserve make the estimate too low.
Apply Epley
100 × (1 + 5 ÷ 30) = 100 × 1.1667 = 116.7 kg.
Check the disagreement
Brzycki and O'Conner both give 112.5, Lander 113.7, Lombardi 117.5. The five span 5 kg, about 4 % — that is the real error bar.
Read the training loads
From a 116.7 kg maximum: 106.1 kg for triples, 100 kg for fives, 87.5 kg for tens. The five-rep load is the weight you actually lifted, which is the arithmetic closing the loop.
Try a longer set
80 kg × 12 spans 102.6 to 115.5 kg — a 13 % disagreement. The equations lose their grip as the set gets longer.
Use the estimate to program, not to prove anything.
The spread is the point. At five repetitions the equations agree within about 4 %, so any of them is fine. At twelve they disagree by 13 %, which is more than a plate. Below about six repetitions, trust the number; above ten, treat it as a rough guide.
Repetitions in reserve break it. These equations assume the set was taken close to failure. Stopping two repetitions early makes a five-rep set behave like a seven-rep set and drags the estimate down. If you are not sure how close to failure you were, assume the estimate is conservative.
It is lift-specific. A squat set predicts a squat maximum, not a bench maximum. Lifts with a large stabiliser demand — overhead work, single-limb variations — tend to run lower than the equations suggest, and leg presses considerably higher.
Never simply load the bar to it. The prediction is a planning tool. If you want a true maximum, work up to it over several sets on a day you are fresh, with a spotter or safeties.
For the calories a session costs, use the Calories Burned Calculator; for the protein that supports the training, the Macro Calculator.
What a prediction equation cannot see
This calculator is for informational purposes and is not medical advice or a diagnosis.
- Accuracy falls with repetitions. Within about 4 % at five repetitions, but a 13 % spread at twelve.
- Training history matters. Well-trained lifters tend to produce more repetitions at a given percentage than novices, which shifts every equation.
- The lift matters. Squat and deadlift usually fit better than bench press; machine and single-limb work fits worst.
- Technique breakdown invalidates it. Repetitions completed with degrading form are not the repetitions the equations were fitted on.
- Fatigue, sleep and time of day move the real maximum by more than the difference between two of these equations.
Warm up thoroughly, use safeties or a spotter for heavy work, and consult a qualified coach or a doctor before maximal testing — especially with a history of injury or a cardiovascular condition.