How a 1RM is estimated
Testing a true one-rep max means loading a bar to near your limit, which is tiring and carries injury risk. Estimation formulas avoid that by predicting your max from a submaximal set: the weight you lifted and how many reps you managed.
This tool shows two well-known formulas. Epley assumes each rep adds a fixed fraction to the load, while Brzycki uses a slightly different curve. They agree closely at low reps and drift apart as reps rise, which is why the comparison is useful.
Why fewer reps give a better estimate
Estimates are most accurate for heavy sets of roughly one to ten reps, where maximal strength is the limiting factor. Past about fifteen reps, muscular endurance and fatigue dominate, so the prediction becomes unreliable. That is why this calculator caps reps at fifteen.
For the cleanest result, use a recent set taken close to failure with strict form rather than an easy set with reps left in reserve.
Using the percentage table and chart
The table and bar chart break your estimated max into common training percentages and the rep ranges they usually support. They make it easy to plan working weights.
- Strength work often sits around 85 to 95 percent for low reps.
- Hypertrophy (muscle-building) work commonly uses 70 to 80 percent.
- Lighter percentages suit technique practice and higher-rep volume.
- Round to weights your plates can actually make.
A note on safety
These are estimates, not guarantees of what you can lift. Always warm up, use a spotter or safety bars for heavy attempts, and stop if form breaks down. If you are new to lifting or returning from injury, get coaching before testing near-maximal loads.
Formula
Epley: 1RM = weight × (1 + reps/30); Brzycki: 1RM = weight × 36 / (37 − reps)Frequently asked questions
- Why limit the reps to 15?
- Estimation formulas are most accurate for sets of about 1 to 10 reps. Beyond roughly 15 reps the estimate becomes unreliable because endurance, not maximal strength, dominates.