Calculators / 1RM calculator
1RM calculator
A one-rep max calculator estimates the most you could lift once from a set you actually did. Enter the weight and the reps, get the estimated 1RM and a rep-max table; flip the direction to turn a known max into the weight for any rep count. Same two formulas as the Zyra Workouts app, numbers never leave your browser.
| Reps | % of 1RM | Weight (kg) | |
|---|---|---|---|
| 1 | 100% | 112.5 | |
| 3 | 94.4% | 106.3 | |
| 5 | 88.9% | 100 | |
| 8 | 80.6% | 90.6 | |
| 10 | 75% | 84.4 | |
| 12 | 69.4% | 78.1 |
How the math works
Two formulas, one switch — the same rule the app applies when it estimates a max from a logged set:
- 1RM = weight × 36 ÷ (37 − reps) — Brzycki, used for sets of 12 reps or fewer
- 1RM = weight × (1 + reps ÷ 30) — Epley, used above 12 reps
- weight for N reps = 1RM × (37 − N) ÷ 36 (N ≤ 12), else 1RM ÷ (1 + N ÷ 30) — the exact inverses, which is what the rep-max table and the reverse direction use
Worked example: 100 kg × 5 reps → 100 × 36 ÷ (37 − 5) = 100 × 36 ÷ 32 = 112.5 kg. The same weight for 13 reps → Epley: 100 × (1 + 13 ÷ 30) = 143.3 kg. This is arithmetic, not a trial result: a population formula is typically a few percent off a tested max, and drifts further the longer the set.
Rep-max table for a 112.5 kg max
| Reps | % of 1RM | Weight (kg) |
|---|---|---|
| 1 | 100% | 112.5 |
| 3 | 94.4% | 106.3 |
| 5 | 88.9% | 100 |
| 8 | 80.6% | 90.6 |
| 10 | 75% | 84.4 |
| 12 | 69.4% | 78.1 |
Percentages are the inverse of the two formulas above, not a separate lookup table — so a row put back through the calculator lands on the same max.
Per-exercise 1RM calculators
The same widget with sensible starting numbers for each lift, plus that exercise's targets, progression step and a link to its load chart:
Frequently asked
How do you calculate a one-rep max from reps?
Two published formulas. Up to 12 reps this calculator uses Brzycki: 1RM = weight × 36 ÷ (37 − reps). Above 12 reps it switches to Epley: 1RM = weight × (1 + reps ÷ 30). A set of 100 kg × 5 reps gives 100 × 36 ÷ 32 = 112.5 kg.
Why does the estimate change formula at 12 reps?
Brzycki divides by (37 − reps), so it climbs steeply as reps rise and is undefined at 37. Epley grows linearly and stays sensible for longer sets. The Zyra Workouts app uses Brzycki through 12 reps and Epley beyond, and this calculator applies the same switch so the numbers match the app.
How accurate is a calculated 1RM?
It is a population estimate, not a tested max. Both formulas were fitted on low-rep sets, which is why the calculator flags anything above 20 reps as unreliable. Sets of 1–5 reps track a real max more closely than sets of 10 or more; the same lifter can also land on different sides of the estimate on different lifts.
What percentage of my 1RM is a 5-rep set?
The inverse of Brzycki: (37 − 5) ÷ 36 = 88.9% of the max. The rep-max table on this page lists 1, 3, 5, 8, 10 and 12 reps the same way, and the per-exercise load charts print every 5% step from 60% to 95%.
Can I use this calculator in pounds?
Yes. Both formulas scale linearly with weight, so the unit does not change the arithmetic. Switch the unit toggle to lb and the fields convert at 2.2046 lb per kg.
Is a 1RM estimate training advice?
No. It is arithmetic on the set you enter. What to do with the number — which percentage to train at, how many sets — is a programming decision for you and your coach. Nothing here is medical advice.
Related calculators
Log the set once, get the estimate every time
Zyra Workouts estimates 1RM from each logged working set with these two formulas and uses it to step the next load. It is in development and not yet on the App Store.
Zyra is a training and nutrition tracking tool. Nothing on this page is medical advice, a diagnosis, or an individual prescription. The numbers are estimates from published formulas and the apps' own rules — consult a qualified professional for decisions about your health, and a coach for your training.