One Rep Max Calculator
Your one-rep maximum (1RM) is the cornerstone of evidence-based strength programming. Enter any submaximal set and this calculator estimates your 1RM using up to seven published formulas, then shows exact training loads for every zone from near-max strength down to muscular endurance. Prefer to work backward? Switch to Reverse mode and enter your 1RM with a target rep count to find the right working weight.
Formula
Worked example
100 kg for 5 reps: Epley 1RM = 100 × (1 + 5/30) = 116.7 kg. Brzycki: 100 × (36/32) = 112.5 kg. Average of all 7 formulas = ~113.5 kg.
How the Calculator Works
This calculator estimates your one-rep maximum from any submaximal set you have already completed. Enter the load you moved and how many reps you completed, choose a formula, and the calculator applies the selected equation. Because no two formulas agree perfectly, the Average option takes the mean of all seven and is generally the most conservative choice for programming purposes. The results panel shows your estimated 1RM and six training-intensity targets from 70% to 95% of that max, each labelled with the zone and approximate rep range they correspond to.
Seven Formulas: Which One Should You Use?
The Epley formula (1 + r/30) is the oldest and most widely cited, published in 1985 and later compared head-to-head against competing equations by LeSuer and colleagues. Brzycki (36/(37-r)) and O'Conner (1 + 0.025r) both produce slightly lower estimates and tend to be more conservative at higher rep counts. Lombardi (r^0.10) increases more steeply with reps and can overpredict at sets above 8. Mayhew and Wathan use exponential decay curves that flatten as reps rise, which some researchers argue better reflects real-world endurance contributions. Lander was derived specifically from free-weight compound lifts. If you are new to 1RM estimation, start with Epley or the Average of all 7 for a balanced result.
Reverse Mode: Finding the Right Working Weight
Reverse mode flips the calculation: instead of estimating your 1RM from a set, you enter a known or previously estimated 1RM and a target rep count, and the calculator solves algebraically for the load that should produce that rep count at your max. This is useful when your coach prescribes a specific intensity percentage or rep scheme and you need to find the bar weight. Select the same formula you used to establish your 1RM for maximum consistency, round the result to a practical plate combination, and aim to stay 1-2 reps short of failure for the most accurate ongoing tracking.
Training Zones: Programming From Your 1RM
Percentage-based programming is the foundation of periodized strength training. At 90-95% of your 1RM you are working in the maximal strength zone, typically 1-3 reps, recruiting the highest-threshold motor units and driving neural adaptations. At 75-85% (5-8 reps) you enter the strength-hypertrophy continuum where both mechanical tension and metabolic stress are high, maximizing muscle growth stimulus. At 65-75% (10-15 reps) the emphasis shifts toward hypertrophy and local muscular endurance. Below 60% loads are typically used for speed-strength work, warm-ups, or high-volume conditioning. The full load table generated by this calculator maps your exact weights to each of these zones.
Accuracy and Limitations
Every regression-based formula carries a standard error of roughly 3-6% under controlled conditions. Accuracy degrades above 10 reps as muscular endurance increasingly determines performance rather than maximal strength. The formulas were validated primarily on compound barbell lifts (squat, bench, deadlift); they are less reliable on isolation exercises or machine-based movements. Individual variation in muscle fiber composition means some lifters consistently over- or under-perform formula predictions. For competitive purposes a directly tested 1RM remains the gold standard, and no calculator should replace a properly supervised maximal attempt.
Formula comparison for 100 kg x 5 reps
| Formula | Equation | 1RM estimate (100 kg x 5 reps) |
|---|---|---|
| Epley | w × (1 + r/30) | 116.7 kg |
| Brzycki | w × 36/(37-r) | 112.5 kg |
| Lombardi | w × r^0.10 | 117.5 kg |
| Mayhew | 100w / (52.2 + 41.9 × e^(-0.055r)) | 116.0 kg |
| O'Conner | w × (1 + 0.025r) | 112.5 kg |
| Wathan | 100w / (48.8 + 53.8 × e^(-0.075r)) | 116.0 kg |
| Lander | 100w / (101.3 - 2.671r) | 112.8 kg |
| Average | Mean of all 7 | 114.9 kg |
All seven prediction equations applied to the same set. Results vary by up to ~6 kg, highlighting why the Average option gives a stable estimate.
Frequently asked questions
How many reps should I use for the most accurate estimate?
Using a weight you can lift for 3 to 5 reps yields the tightest predictions, because at that rep range the set is genuinely strength-limited rather than endurance-limited. Sets of 2 reps or even 1 rep work too (the formula still runs), but the value of a prediction decreases as reps approach 1. Sets above 10 reps meaningfully increase error, so avoid using high-rep sets if accuracy matters.
Which formula is most accurate?
Research by LeSuer et al. (1997) comparing seven formulas on college-aged powerlifters found that the Epley, Brzycki, and Mayhew equations performed most consistently for the squat, bench press, and deadlift. No single formula dominates across all populations and exercises, which is why the Average option provides a useful middle estimate. Try a set at a known weight and compare the predicted 1RM against a tested max to discover which formula tracks your individual performance best.
Can I use my estimated 1RM to program all my training sets?
Yes, percentage-based programming from an estimated 1RM is standard practice in powerlifting and strength and conditioning. Reassess your 1RM every 4 to 8 weeks, or whenever you complete a training cycle, to keep the percentages aligned with your current strength level. Many coaches also apply a small deduction (2-5%) to the estimated 1RM as a safety buffer when writing high-intensity blocks.
What is Reverse mode and when should I use it?
Reverse mode inverts the calculation: you enter a known 1RM and a target number of reps, and the calculator solves for the working weight. Use it when your program specifies a set at a given rep count and you need to know what to put on the bar. For example, if your coach writes "4 sets of 6 at roughly 80% of 1RM" and you know your bench press 1RM is 120 kg, reverse mode gives you the exact working weight without manual arithmetic.
Does the exercise type change the calculation?
The Exercise selector in this calculator labels your result for the insight panel but does not change the math, because the published formulas are exercise-agnostic regression equations. Some research (notably NSCA guidelines) does publish exercise-specific coefficient tables for squat, bench, and deadlift, but the differences are small (typically 1-3 kg) and within the normal prediction error. Selecting the correct exercise mainly helps you keep track of multiple lifts across sessions.
How do I convert between kg and lb?
Switch the Units selector at the top of the calculator. All inputs and outputs update immediately to the selected unit. If you enter your weight in lb, your 1RM and all percentage targets are also shown in lb. One kilogram equals 2.2046 pounds; one pound equals 0.4536 kilograms.
Sources
- LeSuer DA et al. The accuracy of prediction equations for estimating 1RM performance in the bench press, squat, and deadlift. J Strength Cond Res. 1997;11(4):218-221.
- Haff GG, Triplett NT (eds). Essentials of Strength Training and Conditioning, 4th ed. NSCA, 2016. Chapter 14: Resistance Training Program Design.