One Rep Max Formulas:
Estimate Your Max
Six widely-used formulas for estimating your 1RM from a submaximal set. How they differ, when to use each, and why 1–5 reps beats anything higher.
What is a 1RM?
Your One Rep Max (1RM) is the heaviest weight you can lift for a single clean repetition with proper form. It is the single most important number in percentage-based strength training — every program that prescribes "work up to 80%" or "do 5 sets at 70%" is scaled from your 1RM.
1RM is specific to the lift: your squat 1RM tells you nothing about your bench, and vice versa. It's also specific to the day: your true max varies by 2–5% between good and bad training days. That's why estimation — based on a heavy set of 3 or 5 — is often a more stable reference than an actual max-out attempt.
Why Estimate Instead of Test?
Testing a true 1RM is useful, but expensive:
- Requires a full warm-up protocol (typically 20–30 minutes)
- Best with a spotter, especially for squat and bench
- Creates meaningful fatigue for several days, which can disrupt serious training during that window
- Most valid when you're fresh, fed, and mentally peaked (rare on a Tuesday evening)
Estimation lets you infer your 1RM from a submaximal heavy set — say, 5 reps at the heaviest weight you can cleanly handle — and plug it into a formula. How close it lands depends on the lift, your rep range, and how near to failure the set was — but for a clean set of 3–5 reps it's usually within a few percent, well inside the variability of max-out attempts themselves.
Rule of thumb: test an actual 1RM a few times a year if you're a competitive powerlifter. For everyone else, estimate from 3–5 rep sets and recalibrate quarterly.
The Six Formulas
These are the six most-used 1RM estimation formulas. Each was derived from a different dataset and gives slightly different numbers. Our 1RM calculator averages all six to smooth out individual formula bias.
Epley (1985)
1RM = w × (1 + r/30) — simple, widely used, tends to overshoot slightly at higher reps. Good default for 1–10 rep estimates.
Brzycki (1993)
1RM = w × 36 / (37 − r) — the most commonly cited formula in the strength research. Slightly lower estimates than Epley. Best accuracy in the 1–10 rep range.
Lombardi (1989)
1RM = w × r^0.1 — sits near the top of the pack at 1–5 reps (just under Mayhew), crosses Brzycki around 7–8 reps, then drops well below it past 10. Used in some older NSCA textbooks.
Mayhew (1992)
1RM = 100 × w / (52.2 + 41.9 × e^−0.055r) — developed specifically for bench press from trained college football players. Tends to predict slightly higher 1RMs than most.
O'Conner (1989)
1RM = w × (1 + r/40) — essentially Epley with a gentler curve. The lowest of the six from about 6 reps up; below that, Brzycki reads slightly lower. Conservative choice for higher-rep estimates.
Wathen (1994)
1RM = 100 × w / (48.8 + 53.8 × e^−0.075r) — very similar in shape to Mayhew, calibrated on a mixed-lift dataset. Commonly appears alongside Brzycki in academic papers.
In all six: w = weight lifted, r = reps performed.
Accuracy & Rep Range
1RM estimates are most reliable in the 1–5 rep range. Above 5 reps, individual differences (muscle-fibre make-up, rep cadence, how close to failure the set was) start to outweigh the formula, and estimates spread wider. The error bands below are rough ballparks, not precise measurements — your real-world accuracy depends on the lift, your training, and how clean the set was.
| Reps | Rough Error Band | Recommendation |
|---|---|---|
| 1–2 | ±1–2% | Most accurate, but risky for ego-lift reasons |
| 3–5 | ±2–4% | Sweet spot. Safe, accurate, practical |
| 6–10 | ±4–7% | Usable but less reliable |
| 11+ | ±8–15% | Don't bother — you're measuring endurance, not strength |
Why 3–5 reps is the sweet spot: you're working at roughly 85–90% of 1RM, which is heavy enough to engage the same neural and muscular patterns as a true max but light enough to complete safely without a spotter. The formulas were calibrated primarily on this range.
Using Your 1RM in Percentage Programs
Once you have an estimated 1RM, almost every percentage-based program is derived from it. Here's a standard percentage chart derived from the calculator output:
| % of 1RM | Typical Rep Range | Use Case |
|---|---|---|
| 100% | 1 | True max, competition lift, RSC peak week |
| 95% | 1–2 | Heavy singles and doubles, near-max practice |
| 90% | 3–4 | Heavy triples, RSC build week |
| 85% | 5–6 | Heavy sets, estimated 5RM range |
| 80% | 7–8 | Smolov Jr. 8×4 day, RSC volume sets |
| 75% | 9–10 | Smolov Jr. 7×5 day, volume work |
| 70% | 11–12 | Smolov Jr. 6×6 day, technique volume |
| 65% | 13–15 | Hypertrophy range, lighter volume work |
| 60% | 16–20 | Deload weight, high-rep work |
Some programs use a Training Max (85–90% of true 1RM) as the reference instead. In 5/3/1 Wendler, for example, the familiar 85/90/95% top sets are percentages of the Training Max — with a 90% TM, those equal roughly 76.5/81/85.5% of true 1RM.
When to Test vs When to Estimate
Test a true 1RM when:
- You're 4–8 weeks into a peaking cycle and want to verify it worked
- You're prepping for a powerlifting meet and need a realistic opener
- You haven't gauged your actual max in over a year
Estimate when:
- You're programming day-to-day percentages
- You don't have a spotter
- You're training alone or in a commercial gym
- You're in a training block with high recovery demand (Smolov Jr., RSC)
Common Mistakes
Using a PR from 6 months ago. If you haven't touched that weight since, it's not your 1RM anymore. Estimate from recent work.
Estimating from 12+ rep sets. The formulas break down above 10 reps. You're measuring endurance, not max strength.
Testing partial-range "records." Half-depth squats or half-range bench are not 1RMs. Test full range or don't test.
Ignoring bar speed. If your estimate set had your last rep moving at 2 inches per second with a rounded back, it's not clean. Redo with a lighter weight.
Treating one formula as gospel. No single formula wins on every lifter and every rep range. Average them, or pick the one that matches your recent lifting feel.
Not recalibrating. Your 1RM changes every 4–12 weeks. If your programming percentages still reference an estimate from January, you're not really training at 85% anymore.
Frequently Asked Questions
What is a 1RM (One Rep Max)?
Your One Rep Max is the maximum weight you can lift for a single clean repetition with proper form. It is the foundation of percentage-based training programs like 5/3/1 Wendler, Smolov Jr., and the Russian Squat Cycle.
Which 1RM formula should I use?
No single 1RM formula is universally most accurate. Epley and Brzycki are among the most commonly used simple formulas, and averaging multiple formulas (as our calculator does) smooths out individual formula bias. For the most reliable estimate, use 1 to 5 reps.
How many reps should I use to estimate my 1RM?
Use 1 to 5 reps for the most reliable estimate. A heavy set of 3 or 5 gives you the best balance of safety and precision. Accuracy drops significantly above 10 reps — the formulas were not built for endurance ranges.
What's the difference between 1RM and Training Max?
Your 1RM is your true maximum for a single rep. A Training Max (used in 5/3/1 Wendler and similar programs) is set intentionally lower — typically 85 to 90 percent of your 1RM — to keep working sets sustainable and allow progression over many cycles.
Should I test my true 1RM instead of estimating?
For most lifters, estimation is safer and nearly as accurate. True 1RM attempts require a spotter, perfect conditions, and a nervous-system peak — and they are only accurate on the day you test. For day-to-day programming, estimation from a heavy set of 3 or 5 is more practical.
Why do different formulas give different numbers?
Each formula was derived from a different dataset — different lifts, different populations, different rep ranges. In the 1–5 rep range Mayhew and Lombardi tend to read highest and Brzycki and O'Conner lowest, with Epley and Wathen in the middle. Averaging them cancels out formula-specific bias.
Estimate Your 1RM Now
Plug in any heavy set and get your estimated 1RM across all six formulas plus the average — with a full percentage table for programming.
Open the 1RM Calculator → Ready to program? Start with 5/3/1 Wendler →- Epley, B. (1985). Poundage Chart. Boyd Epley Workout, Lincoln, NE.
- Brzycki, M. (1993). Strength Testing — Predicting a One-Rep Max from Reps-to-Fatigue. JOPERD 64(1): 88–90.
- Lombardi, V.P. (1989). Beginning Weight Training. Dubuque, IA: Wm. C. Brown.
- Mayhew, J. L., et al. (1992). Muscular Endurance Repetitions to Predict Bench Press Strength. JSCR 6(4): 200–206.
- O'Conner, B., Simmons, J., & O'Shea, P. (1989). Weight Training Today. St. Paul: West.
- Wathen, D. (1994). Load Assignment. In Baechle, T.R. (Ed.), Essentials of Strength Training and Conditioning. Champaign, IL: Human Kinetics, 435–439.