One-Rep Max Calculator Guide: Estimating Your 1RM一次最大重复(1RM)计算器指南：估算你的极限重量
Your one-rep max (1RM) is the heaviest weight you can lift for a single repetition of an exercise with proper form. It's the foundation of every strength-training program — but you should rarely test it directly. The math behind estimating your 1RM from submaximal work, the percentage tables that turn it into programming, and the limits of the formulas are what this guide covers.
What Is a 1RM?
Your 1RM (one-rep max) is the maximum amount of weight you can lift once, with good form, before failure. It varies by exercise — your bench 1RM, squat 1RM, and deadlift 1RM are three different numbers, often related but never identical.
Testing your true 1RM is fatiguing, injury-prone, and requires a long recovery. That's why strength coaches almost always estimate it from submaximal sets instead.
The Epley Formula — Most Common
The most widely used 1RM estimation formula, developed by Boyd Epley in 1985:
For 1 rep, gives exactly the weight lifted. For 10 reps of 100 lbs: 100 × (1 + 10/30) = 100 × 1.333 ≈ 133 lbs.
Worked example: you squat 225 lbs for 5 reps. Your estimated 1RM:
1RM = 225 × (1 + 5/30) = 225 × 1.167 ≈ 263 lbs
The Epley formula is most accurate for 1–10 rep sets. Beyond 10 reps, it increasingly overestimates true 1RM.
The Brzycki Formula — Slightly More Conservative
Another popular formula, also from the 1980s, that gives marginally lower estimates:
For 5 reps of 225 lbs: 225 × 36 / (37 − 5) = 225 × 36/32 = 253 lbs.
The same 5 reps at 225 lbs gives 263 lbs (Epley) vs 253 lbs (Brzycki) — a 4% difference. For most purposes, both are useful; pick one and stick with it for consistency.
Comparing the Common Formulas
For a hypothetical 200 lbs × 10 reps, the formulas diverge:
| Formula | Estimated 1RM |
|---|---|
| Epley | 267 lbs |
| Brzycki | 270 lbs |
| Lander | 253 lbs |
| Lombardi | 256 lbs |
| O'Conner | 250 lbs |
| Mayhew | 240 lbs |
The spread is roughly 12% — significant when you're choosing training weights. Most calculators let you select which formula to use; the Epley is the safest default.
Rep Max Percentage Tables
The inverse of 1RM estimation is training by percentage of 1RM. If your 1RM squat is 300 lbs, your working weights for various rep targets are:
| Reps | % of 1RM | Weight (300 lb 1RM) |
|---|---|---|
| 1 | 100% | 300 lbs |
| 2 | 95% | 285 lbs |
| 3 | 93% | 279 lbs |
| 5 | 87% | 261 lbs |
| 8 | 80% | 240 lbs |
| 10 | 75% | 225 lbs |
| 12 | 70% | 210 lbs |
| 15 | 65% | 195 lbs |
| 20 | 60% | 180 lbs |
This table is the basis for programs like 5/3/1, Starting Strength, and most periodized training plans. The percentages vary by source but stay within ±5%.
What "nRM" Really Means
A "5RM" (5-rep max) is the most weight you can do for exactly 5 reps with good form — not 6, not 4. The distinction matters for testing:
- If you hit 5 reps and could have done more, your 5RM is actually higher.
- If you hit 5 reps but your 6th-rep form broke down, that is your 5RM.
- Most lifters overestimate by failing to track strict form on the last rep.
For best estimates, work up to a true nRM where you couldn't have done one more clean rep.
A true 1RM attempt is highly fatiguing and takes 5–7 days to fully recover from. Most strength programs test or estimate 1RM only every 4–12 weeks. For weekly training, work in the 70%–85% range for multiple sets of 5–10.
Why Formulas Differ by Exercise
1RM formulas are mostly derived from bench press and squat data. They work best for these compound barbell lifts. For isolation exercises (bicep curls, leg extensions), the formulas are less reliable — a 10-rep set of bicep curls is much closer to a true 1RM than a 10-rep set of squats.
For deadlifts specifically, the formulas tend to underestimate — a 5RM deadlift often translates to a higher actual 1RM than the formulas predict.
Try It
Use the One-Rep Max Calculator to:
- Estimate your 1RM from any submaximal set (1–15 reps).
- See the estimate across all major formulas side-by-side.
- Generate a percentage table for training, with your working weights at every rep target.
The calculator supports multiple formulas (Epley, Brzycki, Lander, Lombardi, O'Conner, Mayhew) and produces a printable percentage table you can use to program your next training block.