One-rep max calculator
Enter the weight you lifted and how many reps you managed. The calculator estimates your one-rep max with the Epley formula and shows useful training loads at 90%, 80%, and 70% of it.
Use it to estimate the most you could lift for a single rep, without testing a true max.
One-rep max
116.7
- 90% (low reps)
- 105
- 80% (strength)
- 93.3
- 70% (volume)
- 81.7
The result updates as you type. The headline is your estimated 1RM; the percentages are practical loads for low-rep, strength, and volume work.
How does it work?
This is the Epley estimate; it is most reliable for about 1–10 reps. At a single rep it returns the weight itself. The result is in whatever unit you enter — kg or lb.
One-rep max (Epley) formula
- 1RM
- Estimated one-rep maximum.
- w
- Weight lifted, in your own unit.
- r
- Reps completed at that weight.
Lifting 100 for 5 reps estimates a 1RM of 100 × (1 + 5/30) ≈ 116.7. At 80% that is about 93.
Method & sources
The Epley formula is used: 1RM = weight × (1 + reps / 30). Weight is unit-agnostic — enter kg or lb and the result follows. Estimates are most reliable for roughly 1–10 reps.
Sources
Where this method comes from — use these references to understand the formula, assumptions, and limits.
- Strength testing — predicting a one-rep max — Brzycki M, NSCA Journal (1993), verified 2026-06-10
How we calculate
- The Epley formula is used: 1RM = weight × (1 + reps / 30).
- Weight is unit-agnostic — enter kg or lb and the result follows.
- Estimates are most reliable for roughly 1–10 reps.
- Percentage loads are simple fractions of the estimated 1RM.
Rounding
Loads are shown to one decimal. The calculation uses full precision.
What this calculator does
Testing a true one-rep max is risky and tiring. Instead, this calculator uses a set you can complete safely — a weight and its reps — and estimates the single-rep maximum with the well-known Epley formula, then scales it to common training percentages.
How to use it
- Enter the weight you lifted, in kg or lb.
- Enter the number of clean reps you completed.
- Read your estimated one-rep max.
- Use the 90/80/70% loads to plan your sets.
A worked example
Lifting 100 for 5 reps gives 100 × (1 + 5/30) ≈ 116.7. That suggests training loads of about 105 at 90%, 93 at 80%, and 82 at 70%.
How accurate is it?
Rep-max formulas are estimates. They are most accurate at lower reps (around 1–10) and can drift on high-rep sets. Treat the number as a guide, not a guarantee, and progress gradually.
Common mistakes
- Counting reps that broke form or used a spotter.
- Using a very high rep set, where the estimate is least reliable.
- Treating the estimate as a max to attempt without building up.
When it's useful
Programming strength training, tracking progress over time, or setting working weights without the risk of a true max attempt.
FAQ
- Which formula does it use?
- The Epley formula: one-rep max equals the weight times one plus the reps divided by 30. At a single rep it returns the weight itself.
- Does it work in kilograms and pounds?
- Yes. The weight is unit-agnostic, so the result is in whatever unit you enter — kg or lb.
- How many reps should I use?
- A set of about 3–8 clean reps gives the most reliable estimate. Very high-rep sets reduce accuracy.
- Should I attempt the estimated max?
- Not without proper warm-up, progression, and ideally a spotter. The estimate is for planning, not a target to test blindly.
- What are the percentage loads for?
- They are common training intensities: around 90% for low reps, 80% for strength work, and 70% for higher-volume sets.
- Can I share a calculation?
- Yes. Use Share to copy a link that reopens the calculator with the same weight and reps.
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