One-Rep Max Calculator — 1RM & Training Loads
Calculate your one-rep max using Epley, Brzycki, Lombardi, and O'Conner formulas. Get full training load percentages for 50–95% of 1RM and compare formulas to find your most accurate estimate.
Exercise Presets (kg)
What Is the One-Rep Max Calculator — 1RM & Training Loads?
The one-rep maximum (1RM) is the heaviest weight you can lift for exactly one repetition with proper form. It is the gold standard for measuring absolute strength and is used to prescribe training loads across all evidence-based strength programmes. Rather than requiring an actual maximum attempt, this calculator estimates your 1RM from a submaximal set — a safer and more practical approach for most athletes.
- ›Four formula comparison — Epley, Brzycki, Lombardi, and O'Conner estimates shown side by side with their average.
- ›Training percentage table — every 2.5% from 50% to 97.5% of 1RM, with target reps and training zone labels.
- ›Plate calculator — shows which plates to load on each side of a standard barbell for key training percentages.
- ›Exercise presets — quick-load typical weights for Bench Press, Back Squat, Deadlift, Overhead Press, and Barbell Row.
- ›Unit toggle — switch between kg and lbs at any time; results update instantly.
Formula
Epley Formula (most widely cited)
1RM = Weight × (1 + Reps / 30)
Brzycki Formula
1RM = Weight × (36 / (37 − Reps))
Lombardi Formula
1RM = Weight × Reps^0.10
O'Conner Formula
1RM = Weight × (1 + Reps / 40)
Average (Primary Result)
1RM = (Epley + Brzycki + Lombardi + O'Conner) / 4
| Formula | Equation | Best For |
|---|---|---|
| Epley | Weight × (1 + Reps/30) | General strength training, most common |
| Brzycki | Weight × 36 / (37 − Reps) | Most accurate for 2–10 reps, breaks above 36 reps |
| Lombardi | Weight × Reps^0.10 | Higher rep ranges (10–20 reps) |
| O'Conner | Weight × (1 + Reps/40) | Conservative estimate, good for beginners |
How to Use
- 1Select a unit: Choose kg or lbs using the toggle at the top.
- 2Enter weight lifted: The load you actually moved — not the bar weight. Enter total weight including the bar.
- 3Enter reps performed: How many reps you completed with that weight. For best accuracy, use a rep count between 2 and 10.
- 4Choose an exercise preset (optional): Click Bench Press, Squat, Deadlift, OHP, or Row to pre-fill typical values.
- 5Press Calculate: Your 1RM estimate (average), all four formula results, training percentage table, and plate calculator appear.
- 6Use the percentage table: Find your target training load for the current training block (hypertrophy, strength, or peaking).
- 7Review plate breakdown: The plate calculator shows which plates to load on each side for any given percentage.
Example Calculation
Bench press: 100 kg for 5 reps
Input: Weight = 100 kg, Reps = 5
Epley: 100 × (1 + 5/30) = 100 × 1.1667 = 116.7 kg
Brzycki: 100 × (36/(37−5)) = 100 × 1.125 = 112.5 kg
Lombardi: 100 × 5^0.10 = 100 × 1.1746 = 117.5 kg
O'Conner: 100 × (1 + 5/40) = 100 × 1.125 = 112.5 kg
Average 1RM = 114.8 kg
| % of 1RM | Weight (kg) | Target Reps | Zone |
|---|---|---|---|
| 60% | 68.9 | 15–20 | Endurance |
| 70% | 80.4 | 10–15 | Hypertrophy |
| 75% | 86.1 | 8–10 | Hypertrophy |
| 80% | 91.8 | 5–8 | Strength |
| 85% | 97.6 | 4–5 | Strength |
| 90% | 103.3 | 2–3 | Peaking |
| 95% | 109.0 | 1–2 | Peaking |
Understanding One-Rep Max — 1RM & Training Loads
Safety Notice
This calculator provides general health and fitness information for educational purposes. It is not a substitute for professional coaching or medical advice. Never attempt a true one-rep maximum without a qualified spotter, proper warm-up, and adequate technique. Estimated 1RM is safest for programming purposes — avoid untested maximal attempts, especially for beginners.
Why Estimate 1RM Instead of Testing It?
A true 1RM test carries injury risk, requires substantial warm-up, is mentally taxing, and can temporarily reduce training quality for several days. Submaximal estimation — performing a near-maximal set of 2–10 reps and applying a formula — is safer and nearly as accurate. Research shows that formula-based estimates are within 5–10% of actual 1RM when reps are kept to 10 or fewer.
Accuracy degrades significantly above 12 reps. Endurance-trained muscles sustain more repetitions at any given percentage of 1RM, causing the formulas to overestimate. For this reason, the calculator flags when rep count is above 10 and recommends testing with 3–6 reps for the most reliable estimate.
The Four Formulas Compared
- ›Epley (1985) — The most widely published formula. Linear relationship between reps and 1RM. Slightly overestimates at higher rep counts. Best overall general-purpose formula.
- ›Brzycki (1993) — Based on a linear model that accounts more for the diminishing returns of higher reps. Mathematically breaks down above 36 reps. Most accurate in the 2–10 rep range.
- ›Lombardi (1989) — Uses a power function (Reps^0.10) rather than a linear model. Performs better at higher rep ranges (10–20) compared to Epley and Brzycki.
- ›O'Conner (1989) — A conservative estimate. Tends to underestimate 1RM slightly, making it the safest choice for programming purposes to avoid overloading.
Training Zone Framework
- ›Endurance zone (50–65% 1RM, 15–25 reps): Builds muscular endurance and work capacity. Often used in general fitness, rehabilitation, or as metabolic conditioning.
- ›Hypertrophy zone (65–80% 1RM, 8–15 reps): The primary range for muscle size development. Supported by decades of bodybuilding research. Also called the "metabolic stress" zone.
- ›Strength zone (80–90% 1RM, 3–8 reps): Develops maximal strength and neuromuscular efficiency. The core of powerlifting-style programming (5×5, 3×3 schemes).
- ›Peaking zone (90–97.5% 1RM, 1–3 reps): Used in competition preparation or testing blocks. High CNS demand — limit frequency, ensure full recovery between sessions.
Related tools
Also useful: Heart Rate Zone Calculator for cardio training zones, and the Calorie Calculator to match your nutrition to training goals.
Progressive Overload and 1RM Re-testing
The 1RM estimate should be re-calculated every 4–8 weeks as strength improves. In a linear progression programme, when you can complete all prescribed reps across all sets with good form, increase the weight by the smallest available increment (typically 2.5 kg / 5 lbs). Re-estimating your 1RM from a freshly completed submaximal set gives you an up-to-date training baseline without the risk of a max test.
Frequently Asked Questions
Which 1RM formula is the most accurate?
- ›Brzycki: most accurate at 2–10 reps
- ›Epley: best all-rounder, slightly overestimates at high reps
- ›Lombardi: better than Epley at 10–20 reps
- ›O'Conner: conservative — good for programming to avoid overloading
- ›Average of four: more robust than any single formula
Why are formulas less accurate above 10–12 reps?
Accuracy drops above 10 reps because:
- ›Muscular endurance (not just strength) increasingly determines rep count
- ›The linear/power relationships in the formulas assume strength-dominant performance
- ›Individual variation in slow-twitch vs. fast-twitch fibre ratio affects high-rep capacity
- ›Best practice: use 3–6 reps for the most accurate 1RM estimate
What is the plate calculator, and how does it work?
The plate calculator:
- ›Subtracts bar weight (45 lbs / 20 kg) from the target load
- ›Divides remaining weight by 2 (one side of the bar)
- ›Uses a greedy algorithm with standard plate sizes
- ›Shows plates per side — load the same on both sides
- ›Works in both kg and lbs depending on unit selection
Should I ever actually test my 1RM in the gym?
- ›Competitive powerlifters: test under meet conditions with a handler and spotters
- ›Recreational lifters: estimated 1RM is accurate enough for programming
- ›Warm-up protocol: 50%×10, 70%×5, 80%×3, 90%×1, 95%×1, then attempt
- ›Take 3–5 minutes rest between heavy warm-up sets
- ›Never attempt true max squats or deadlifts without experienced spotters or safety equipment
How often should I update my 1RM?
- ›Beginners: monthly or when adding weight each session (linear progression)
- ›Intermediate: every 4–6 weeks at the end of a mesocycle
- ›Advanced: every 8–12 weeks, or ahead of competition peaking blocks
- ›Re-estimate after any deload week or return from injury
What weight should I use for a submaximal test to estimate 1RM?
- ›Ideal rep range: 3–6 reps (within 5% of actual 1RM)
- ›Stop 1 rep short of failure (RPE 9 / RIR 1) for best data
- ›Avoid testing to failure — fatigue inflates rep count artificially
- ›Rest fully (5 minutes) before the test set — any fatigue distorts the estimate
- ›Warm up properly: 5–6 ramp sets before the test set
Does 1RM differ between exercises?
1RM is lift-specific and individual:
- ›Lower body lifts (squat, deadlift) are typically stronger than upper body lifts
- ›The "big three" (squat, bench, deadlift) are most commonly tracked in strength sports
- ›Overhead press 1RM is typically 60–70% of bench press 1RM for most athletes
- ›Track each lift separately — one 1RM does not transfer to another exercise