Estimate your one-rep max (1RM) without going to absolute failure. Enter the weight you lifted and the reps you completed; the calculator returns 1RM estimates from four trusted formulas - Epley, Brzycki, Lombardi, and O'Conner - along with the percentages for common rep ranges.
The actual weight on the bar (or dumbbells).
Most accurate at 2–10 reps. Higher reps add error.
Estimated 1RM (average)
91.8 kg
Mean of 4 formulas
Lifted today
80.0 kg × 5 reps
Formula breakdown
Training percentages of your 1RM
| Reps | % 1RM | Weight |
|---|---|---|
| 1 | 100% | 91.8 kg |
| 2 | 95% | 87.2 kg |
| 3 | 93% | 85.4 kg |
| 4 | 90% | 82.6 kg |
| 5 | 87% | 79.9 kg |
| 6 | 85% | 78.1 kg |
| 8 | 80% | 73.5 kg |
| 10 | 75% | 68.9 kg |
| 12 | 70% | 64.3 kg |
| 15 | 65% | 59.7 kg |
1RM estimates are accurate within 2–5% at 2–10 clean reps. Always warm up well, use safety pins or a spotter, and avoid attempting true maxes when fatigued or injured.
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One-rep max (1RM) - the maximum weight you can lift for exactly one repetition with proper form - is the foundational strength metric in resistance training. Every serious strength program prescribes loads as percentages of 1RM: 60-70% for hypertrophy/volume work, 75-85% for strength work, 85-95% for power and peaking. Knowing your 1RM is essential for prescribing the right loads; but actually testing your 1RM is risky (form breakdown at extreme loads can cause injury) and shouldn't be done frequently. This calculator estimates 1RM from a submaximal set, letting you program training without grinding for true singles.
The calculator runs four established formulas - Epley, Brzycki, Lombardi and O'Conner - and shows all four results side-by-side. These formulas were derived from different datasets of competitive lifters and diverge slightly at extreme rep ranges. For typical 2-10 rep submaximal sets, all four agree within ±2-3 kg. The average across formulas is usually the most accurate estimate. The accompanying percentage table tells you what weight to use for any target rep range - invaluable for structured strength programming.
Enter the weight you lifted (in kg or lb).
Enter the number of reps you completed at that weight (most accurate at 2–10 reps).
View 1RM estimates from each formula - they should agree within ~5%.
Use the % table to plan training sets at 60–95% of 1RM.
Each formula was derived from data on how strength scales with reps. They all agree that as you do more reps, the percentage of your 1RM you can move drops in a predictable way. Estimates are most reliable at 2–10 reps; beyond that, fatigue and form breakdown introduce big errors.
Epley: 1RM = w × (1 + r/30) Brzycki: 1RM = w × 36 / (37 − r) Lombardi: 1RM = w × r^0.10 O'Conner: 1RM = w × (1 + 0.025·r)
All four formulas express the same relationship: the more reps you can do at a given weight, the smaller that weight is as a percentage of your 1RM. Epley's formula (1RM = w × (1 + r/30)) is the most-cited and accurate across the typical 1-10 rep range. Brzycki (1RM = w × 36 / (37 − r)) tends to slightly underestimate at low reps and overestimate at high reps. Lombardi and O'Conner give a third and fourth perspective; their average smooths individual formula biases.
Accuracy is highest at 2-10 reps to failure. Below 2 reps, you're essentially testing 1RM directly. Above 10 reps, fatigue accumulates non-linearly, form breaks down, and energy systems shift from anaerobic to aerobic - making 1RM extrapolation unreliable. For best results, work up to a weight you can complete 3-6 strict reps with at full effort (RPE 9-10), then feed those numbers into the calculator.
Strength percentages of 1RM map roughly: 100% = 1 rep, 95% = 2 reps, 90% = 4 reps, 85% = 6 reps, 80% = 8 reps, 75% = 10 reps, 70% = 12 reps, 65% = 15 reps, 60% = 20 reps. These are approximate; individual variation is ±5-10%. Compound lifts (squat, deadlift, bench press) follow these percentages reliably; isolation lifts (curl, lateral raise) sometimes diverge - fewer total muscle fibres recruit per rep, so percentages skew slightly.
Epley: 80 × (1 + 5/30) = 93.3 kg. Brzycki: 80 × 36/32 = 90 kg. Lombardi: 80 × 5^0.10 = 93.6 kg. O'Conner: 80 × 1.125 = 90 kg. Average ≈ 91.7 kg. Working sets at 75% 1RM = 69 kg for 10 reps; at 85% = 78 kg for 6 reps; at 90% = 82 kg for 4 reps.
If you had 1 more rep in tank, you'd have done 4 strict reps to failure. Use 4 reps in the formula. Epley: 120 × (1 + 4/30) = 136 kg. Average across formulas ≈ 134 kg. Use 134 kg as 1RM for programming. Note: estimating from non-failure sets (RPE 8 or below) using 'reps in reserve' is a common safer approach than going to absolute failure each time.
Each formula was fit to a different dataset of lifters. They diverge slightly at low and high rep ranges. Looking at the average gives a balanced estimate.
Within 2–5% of an actual 1RM test for most lifters when reps are between 2–10 and form stays clean. Beyond 10 reps, accuracy drops because fatigue is more variable.
Most lifters don't need to. Estimating 1RM lets you program training percentages without risking injury. Powerlifters and Olympic lifters do test their 1RM, but not weekly - usually once every 8–16 weeks.
Any compound or isolation lift - squat, bench press, deadlift, overhead press, rows. Avoid using these formulas on highly technical lifts (Olympic snatch/clean) where form matters more than absolute strength.
RPE (Rate of Perceived Exertion) is a 1–10 scale of how hard a set felt. RPE 10 is true failure (1RM). RPE 8 means you had 2 reps left. Many programs use RPE-based loads instead of strict %1RM.
For beginners, 1RM can rise weekly. Intermediate lifters add 2–5% per training cycle (4–8 weeks). Advanced lifters may add only 1–2% per cycle. Track over months, not days.
Body composition, daily energy needs and pregnancy timelines all rest on formulas validated across millions of people, but no single number tells the whole story. The values from this calculator are point estimates with a known margin of error - body fat from skinfold or US Navy method has roughly a ±3% standard error compared to a DEXA scan, and BMR can vary ±10% person to person at the same height and weight. Use these numbers to track trends week over week, not to chase decimal precision day to day.
Pair this tool with the BMR, TDEE, calorie and macro calculators to turn a single measurement into an actionable plan. None of these tools are a substitute for a qualified doctor, registered dietitian or certified strength coach - but they remove the busywork so you spend more time on training and recovery, less on math.
The One Rep Max Calculator is part of the Health & Fitness suite on Online Calculator Tools, alongside 6 related calculators. All tools share the same UI patterns, the same privacy-first rendering (nothing is sent to a server), and the same commitment to showing the formula and assumptions behind every result.
