One-Rep Max Calculator
Estimate 1RM strength benchmark using Epley & Brzycki formulas.
This 1rm calculator (one rep max calculator) estimates your one-rep max strength - the heaviest weight you could lift for a single repetition - from a lighter weight lifted for multiple reps, using the Epley and Brzycki formulas. It works for any major lift: bench press, squat, or deadlift.
Enter the weight you lifted and the number of reps you completed, and the calculator estimates your 1rm max.
Worked Calculation Examples
| Scenario | Result | Calculation Step |
|---|---|---|
| 185 lbs for 5 reps | Epley ≈ 216 lbs · Brzycki ≈ 208 lbs | Epley: 185 × (1 + 5/30) = 185 × 1.1667 ≈ 216 lbs. Brzycki: 185 × 36 ÷ (37−5) = 185 × 1.125 ≈ 208 lbs. |
| 225 lbs for 8 reps | Epley ≈ 285 lbs · Brzycki ≈ 279 lbs | Epley: 225 × (1 + 8/30) = 225 × 1.2667 ≈ 285 lbs. Brzycki: 225 × 36 ÷ (37−8) = 225 × 1.2414 ≈ 279 lbs - the two formulas diverge slightly more at 8 reps than they did at 5. |
Why Estimate Instead of Test Directly
Testing a true 1 rep max carries higher injury risk and requires significant warm-up and recovery, so most lifters estimate it from a submaximal set instead - typically 3 to 10 reps at a challenging but manageable weight. The Epley formula (weight * (1 + reps/30)) and Brzycki formula (weight * 36 / (37 - reps)) are the two most common estimation methods, and they tend to agree closely for rep ranges under about 10. Strength coach Boyd Epley developed his namesake formula at the University of Nebraska in the 1980s from empirical data relating submaximal lifts to true one-rep maxes across many athletes, making it possible to estimate maximum strength safely without the injury risk of testing a true single-rep maximum lift directly.
Using Your 1RM for Training Percentages
Once you have a 1rm estimator result, many training programs prescribe work sets as a percentage of it - for example, 5 sets of 5 at 80% of 1RM. This is why an accurate estimate matters: an inflated 1RM leads to overly heavy prescribed training weights, while an underestimated one leaves potential strength gains on the table.
How to Use the One-Rep Max Calculator
- Open the One-Rep Max Calculator and enter the values requested in the input fields.
- Check the units, percentages, dates, or time periods before reading the answer.
- Review the instant result and adjust any value to compare another scenario.
- Use the formula, example, and FAQs below to understand how the 1rm calculator works.
Frequently Asked Questions
How do I calculate my 1 rep max without lifting it directly?
Use the Epley formula: 1RM = weight * (1 + reps/30), based on a lighter set of a known weight and rep count.
Which formula is more accurate, Epley or Brzycki?
Both give similar results for sets of about 10 reps or fewer; Epley tends to estimate slightly higher for higher rep counts, while Brzycki is often considered more accurate specifically in the 1-10 rep range.
How accurate is a 1rm estimator?
It's a reasonable approximation for most lifters, typically within a few percent of an actual tested max, though individual fatigue resistance and technique can shift the real number in either direction.
How do I use this 1rm calculator?
Enter the known values, review the units or settings, and the calculator updates the result instantly. The formula and example on this page show how the answer is produced.
What does the One-Rep Max Calculator calculate?
Estimate 1RM strength benchmark using Epley & Brzycki formulas. It is designed for fast browser-based calculations without sign-up, downloads, or manual spreadsheet setup.
What formula does this one-rep max use?
The formula is: Epley: 1RM = Weight × (1 + Reps ÷ 30); Brzycki: 1RM = Weight × 36 ÷ (37 − Reps). Weight is the load lifted for the set, and Reps is how many repetitions were completed with that weight. Both formulas extrapolate from a submaximal set to estimate the heaviest weight liftable for exactly one repetition. They agree closely under about 10 reps but diverge more at higher rep counts, which is why both are typically most accurate for sets in the 1-10 rep range.
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Last updated: September 29, 2026.