One Rep Max (1RM) Calculator
Estimate your one-rep max from a weight you can lift for multiple reps, and get a full percentage training chart.
How to use the one rep max calculator
- Enter the weight you lifted and how many reps you completed.
- Choose your unit (kg or lb).
- Click Calculate to see your estimated 1RM and percentage chart.
Using percentages to program your training
Many strength programs prescribe loads as a percentage of 1RM — for example 5 sets of 5 at 80%. The chart this tool produces lets you turn your estimated max into concrete working weights for each rep range.
Why estimate a 1RM instead of testing it
Testing a true one-rep max is fatiguing and carries injury risk, especially for newer lifters or anyone training alone. Estimating it from a set you can complete with good form gives you almost the same programming value without the danger.
Estimates are most accurate in the 2-5 rep range. Above about ten reps, fatigue and technique breakdown make the prediction drift, so use a heavier, lower-rep set when you want a reliable number.
Using percentages to program your lifts
Most strength programs prescribe load as a percentage of 1RM: a hypertrophy block might sit at 67-75%, while a strength block lives at 85% and above. The percentage chart this tool produces turns your estimated max into concrete working weights for every rep range, so you can plan a full mesocycle from a single test set.
Reps to percentage of 1RM
| Reps to failure | % of 1RM | Main training focus |
|---|---|---|
| 1 | 100% | Maximal strength |
| 2 | 95% | Maximal strength |
| 3 | 93% | Strength |
| 4 | 90% | Strength |
| 5 | 87% | Strength |
| 6 | 85% | Strength / hypertrophy |
| 8 | 81% | Hypertrophy |
| 10 | 75% | Hypertrophy |
| 12 | 71% | Hypertrophy / endurance |
| 15 | 67% | Muscular endurance |
Approximate population averages — individuals vary, and the estimate drifts beyond about ten reps as endurance and technique start to limit the set before strength does.
Frequently asked questions
How is one-rep max calculated?
1RM is estimated from submaximal lifts using formulas like Epley (weight × (1 + reps/30)). This tool averages several validated formulas for a robust estimate.
How many reps should I use for an accurate 1RM?
Estimates are most accurate at 2–5 reps. Above about 10 reps, fatigue and technique reduce accuracy.
How many reps give the most accurate 1RM estimate?
Sets of 2-5 reps are most accurate. The further you go beyond five reps, the more the estimate underpredicts, because endurance and technique start to limit the set before true strength does.
Which 1RM formula is best?
Epley and Brzycki are the most widely used and agree closely at low reps. Averaging several formulas, as this tool does, smooths out their individual quirks.
Should beginners test or estimate their 1RM?
Beginners should almost always estimate. Form is still developing, and a maximal single is both risky and unreliable until technique is consistent.
What percentage of my 1RM should I lift for muscle growth?
Hypertrophy work typically sits around 67–80% of your 1RM, roughly the 8–12 rep range in the chart below. Pure strength work lives at 85% and above, and muscular endurance below about 67%.
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