One Rep Max Calculator
Testing a True Max Isn't Always the Right Call
Finding out exactly how much you can lift for a single rep usually means loading a bar heavy enough to risk a missed attempt, which is why most lifters estimate it instead. One-rep max prediction formulas take a lighter, safer set — say five or eight reps — and extrapolate what a true single-rep max would likely be, based on well-documented relationships between reps performed and percentage of max strength.
The Formulas
This calculator offers three established prediction formulas:
Brzycki: 1RM = Weight × (36 ÷ (37 − Reps))
Lombardi: 1RM = Weight × Reps^0.10
Each formula extrapolates differently as rep count rises — Epley scales roughly linearly, Brzycki curves more sharply as reps approach its 37-rep ceiling, and Lombardi grows more slowly at high rep counts. If exactly one rep was performed, the entered weight is simply reported as-is, since no extrapolation is needed.
Where This Calculation Matters
- Programming training percentages — most strength programs prescribe work sets as a percentage of 1RM, so an accurate estimate is the foundation the whole program is built on.
- Avoiding unnecessary max-effort testing — estimating from a submaximal set avoids the injury risk and fatigue cost of testing a true single-rep max directly.
- Tracking strength over time — recalculating estimated 1RM from regular training sets shows strength trends without needing a dedicated max-out session every time.
- Comparing lifts across rep ranges — converting different rep-range work back to a common 1RM estimate makes otherwise incomparable sets comparable.
Estimated 1RM by Formula (100 kg for 5 and 10 reps)
Applying all three formulas to the same lifted weight shows how their extrapolations diverge as reps increase:
| Reps performed | Epley | Brzycki |
|---|---|---|
| 5 | 116.7 kg | 112.5 kg |
| 10 | 133.3 kg | 133.3 kg |
All formulas are estimates, not guarantees — individual fatigue tolerance and lift technique affect how closely a real max matches the prediction.
How to Use This Calculator
- Select the unit — Metric (kg) or Imperial (lb).
- Select the formula — Epley, Brzycki, or Lombardi.
- Enter the Weight Lifted and Reps Performed.
- Select Calculate to see your estimated one-rep max along with a full rep-range percentage chart.
Related Calculations
To compare relative strength against bodyweight in a competition context, see the Powerlifting Score Calculator. To estimate the calories burned during a strength session, check the Exercise Calorie Estimator.