1RM Calculator (One Rep Max)
🏋️ Free 1RM calculator using the Epley formula. Enter any weight and reps and get your estimated one rep max plus 3RM, 5RM, 8RM, 10RM and 12RM for programming.
- Data verified · June 2026
- Edited by Martín Rodríguez
- Formula verified by automated tests
- Private — runs on your device
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How to use this calculator
Follow this tool’s steps, then review its formula, assumptions, and limits below.
When to use this calculator
- You want to know your 1RM without actually testing it (safer + less fatiguing).
- You're programming a training cycle and need your max to compute % loads.
- You're competing in powerlifting and need attempt openers.
- You're tracking strength progress week to week.
- Your coach asks for % of 1RM and you only know "how much you lifted for 5 reps".
%1RM Training Zones (NSCA)
| %1RM | Reps estimados | Objetivo de entrenamiento |
|---|---|---|
| 100% | 1 | Máximo real |
| 95–97% | 2–3 | Fuerza neural |
| 90–93% | 3–5 | Fuerza pesada |
| 80–87% | 5–8 | Fuerza + hipertrofia |
| 70–80% | 8–12 | Hipertrofia |
| 60–70% | 12–15 | Resistencia muscular |
| <60% | 15+ | Acondicionamiento / calentamiento |
Fuente: NSCA — Essentials of Strength Training and Conditioning, 4th ed. (nsca.com)
How it works
The Epley formula
1RM = weight × (1 + reps / 30)
Developed by Boyd Epley (University of Nebraska strength coach) in 1985, this formula is the most widely used 1RM estimator in strength and conditioning. It's accurate within ±3–5 % of your actual 1RM when the submaximal set is performed in the 3–6 rep range.
Above 10 reps the estimate becomes unreliable because endurance-type sets depend more on glycolytic capacity than on maximal strength. If you care about a precise 1RM, work up to a heavy triple or single rather than plugging a 12-rep set.
How the math works (quick example)
You bench press 100 kg × 5 reps:
> 1RM = 100 × (1 + 5 / 30) = 100 × 1.167 = 116.7 kg
Each rep beyond the first adds roughly 3.3 % to the estimated max. That's why a 10-rep set doesn't just add a little error — it compounds across all ten increments, inflating the result significantly.
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%1RM training zones (NSCA)
| %1RM | Reps | Training goal |
|---|---|---|
| 100 % | 1 | True max |
| 95–97 % | 2–3 | Neural strength |
| 90–93 % | 3–5 | Heavy strength |
| 80–87 % | 5–8 | Strength + size |
| 70–80 % | 8–12 | Hypertrophy |
| 60–70 % | 12–15 | Muscular endurance |
| < 60 % | 15 + | Conditioning / warm-up |
Practical use: if your estimated 1RM is 120 kg and you're in a hypertrophy block, you'd train at 70–80 %, meaning 84–96 kg for sets of 8–12. Recalculate every 4–6 weeks or after a significant strength jump.
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Is Epley the best formula?
It's one of several validated options. Others:
1RM = weight × 36 / (37 − reps). Nearly identical to Epley for ≤ 10 reps; diverges faster at higher rep counts.1RM = weight × reps^0.1. Tends to over-predict for high reps (> 8).1RM = weight × (1 + reps / 40). More conservative; may underestimate for well-trained lifters.For rep ranges of 3–8, all four agree within a couple of percent. A 2020 review in the Journal of Human Kinetics confirmed that no single formula consistently outperforms the others across all exercises and populations — accuracy depends more on the rep range used than on the specific equation.
Epley remains the most popular because the arithmetic is easy to approximate mentally and it was the first to be widely adopted in US collegiate strength programs.
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What the calculator does NOT include
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Common errors that skew the result
| Error | Effect on estimate |
|---|---|
| Stopping before true failure (leaving 3+ RIR) | Underestimates 1RM |
| Bouncing the bar or using momentum | Overestimates 1RM |
| Using > 10 reps as input | Usually overestimates 1RM |
| Comparing estimates across different exercises | Meaningless — each lift has its own strength curve |
| Treating the estimate as a hard max for singles day | Injury risk — always approach a true 1RM attempt with proper warm-up and spotters |
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When to use a true 1RM test instead
Estimated 1RMs are fine for programming purposes. For competition prep, official records, or medical/research protocols, a supervised single-rep max test is the standard. The general warm-up protocol recommended by the NSCA:
1. 40–60 % × 5 reps
2. 60–80 % × 3 reps
3. 80–90 % × 1 rep
4. Attempt 1RM; rest 3–5 min between attempts
5. Adjust up or down in ~2.5–5 % increments
For most recreational lifters, the calculator result is precise enough to set training loads — and safer than frequent maximal attempts, which carry a higher injury risk with no additional hypertrophy benefit.
Example: 100 kg × 5 reps (back squat)
Frequently asked questions
How do you calculate 1RM from reps?
How many reps should I use for the most accurate 1RM estimate?
Is Epley more accurate than Brzycki?
Can I use this for bench press, squat and deadlift?
Should I actually test my 1RM?
What's the difference between RM, %1RM, and RPE?
Why does the calculator ask for kg or lb?
My calculated 1RM seems too high. Why?
Sources & references
Methodology & trust
Sports calculator with its formula verified automatically against Epley, B. (1985). Poundage chart. Boyd Epley Workout., per our editorial policy and methodology.
Updated: June 27, 2026. Parameters are verified periodically against the cited sources.
Calculations run 100% in your browser. We do not store or transmit your data.
Indicative results. For critical decisions, consult a professional.
Rodríguez, M. (2026). 1RM Calculator (One Rep Max). Hacé Cuentas. https://hacecuentas.com/en/1rm-calculator
Content licensed under CC-BY 4.0 — reuse it citing the source with a link to Hacé Cuentas.