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The calculator applies the Epley formula from 1985: 1RM = weight × (1 + reps/30), where weight is what you lifted and reps is how many clean repetitions you completed. Each rep adds about 3.33% to the estimated max. The formula is most accurate for sets of 2 to 10 reps taken close to failure on standard barbell lifts; outside that window the estimate drifts, because high-rep sets measure endurance as much as strength. The calculator is unit-agnostic: enter kilograms or pounds and the result uses the same unit. An estimated 1RM is a planning tool, not a measurement, so never attempt the number without a spotter.
The Epley formula (Boyd Epley, 1985) is the most widely used 1RM estimator in strength training:
1RM = weight × (1 + reps / 30)
Each rep you complete adds roughly 3.33% to the estimated max. The formula is fitted to real lifter data: it models the observed relationship between a submaximal load and the number of reps lifters typically manage with it. Worked example: bench press 80 kg for 8 reps gives 80 × (1 + 8/30) = 80 × 1.2667 = 101.3 kg estimated 1RM. The formula reverses cleanly, which is how training weights are programmed: weight for a target rep range = 1RM / (1 + reps/30). So with a 100 kg estimated max, sets of 5 should be loaded at 100 / 1.1667 = 85.7 kg.
Epley is not the only published formula, and the research disagrees about which fits best:
Epley (1985): 1RM = weight × (1 + reps/30). Linear, the default in most programs including 5/3/1, strongest research support in the 3-8 rep range.
Brzycki (1993): 1RM = weight × 36 / (37 - reps). Slightly more conservative, often closest at 10 reps or fewer, fitted on bench press data.
Lombardi (1989): 1RM = weight × reps⁰.10. Exponential, tends to sit near Epley at low reps.
At 2 to 5 reps the formulas land within a few percent of each other; at 12 reps they spread by more than 12%. That is the argument for keeping test sets short rather than hunting for the right formula. This calculator uses Epley because it has the broadest support across the major lifts.
Your estimated 1RM converts into training weights by running Epley backwards. Percentage of 1RM at reps n = 100 / (1 + n/30). Use this 1RM percentage chart to set working weights for every rep range:
1 rep: 100% (true max attempt) 2 reps: 95% (heavy doubles, peak strength) 3 reps: 91% (heavy triples, peaking) 4 reps: 88% 5 reps: 86% (strength work, 5/3/1) 6 reps: 83% (strength-hypertrophy crossover) 8 reps: 79% (hypertrophy, top end) 10 reps: 75% (hypertrophy and volume) 12 reps: 71% (hypertrophy-endurance crossover)
Programming guide: raw strength 85-90% for low reps, hypertrophy 65-75% for 8-12 reps, power and speed 50-60% moved fast. Many coaches use a training max of 90% of the estimated 1RM so you can hit your numbers even on a bad day.
Four rules for a number you can trust:
1. Use 2 to 10 reps, ideally 3 to 8. Below 2 reps Epley overestimates; above 10, muscular endurance dominates and the estimate drifts high. A 12+ rep set measures conditioning as much as strength.
2. Take the set close to failure, with 1 to 2 reps in reserve at most. Stopping 5 reps short understates your true max significantly.
3. Keep form honest. Full range of motion, no spotter touching the bar, no half-reps: the formula assumes the set you entered was a real set.
4. Match the lift. Your 1RM differs by exercise, so estimate separately for bench, squat, deadlift, and overhead press rather than carrying one number across lifts. Deadlift estimates run slightly less accurate than squat or bench because deadlift strength drops off faster with fatigue.
An estimated 1RM is a prediction from a set you did, not a measurement, so you can plan heavy training without maxing out. Your real max moves with sleep, stress, technique, and the day, which is exactly why most people train off an estimate instead of testing often. If you do test a true single: warm up thoroughly, use a spotter or safety pins, rest 2 to 5 minutes between attempts, and increase the weight gradually. Beginners should skip max testing entirely and focus on form; the formula gives them the same programming information at a fraction of the injury risk. Note one quirk: entering a true single (1 rep) into Epley estimates about 3% above the weight you lifted, because the formula is fitted to multi-rep sets. If you have actually tested a single, that number is your max, and no formula improves on it.
Enter the weight you lifted (kilograms or pounds, the result uses the same unit), the number of reps you completed with good form, and press calculate. The calculator returns your estimated one-rep max from the Epley formula. Compare the result to the training percentage table above to pick working weights for your program, and re-run it every few weeks to track progress across mesocycles.
A one-rep max (1RM) is the heaviest weight you can lift for a single repetition of a specific exercise with good form. It is the standard reference point for setting training loads, because most programs are written as percentages of it, and it lets you track strength progress over time.
Multiply the weight you lifted by (1 + reps/30). For example, 100 kg for 5 reps gives 100 × 1.1667 = 116.7 kg. This is the Epley formula (1985), the most widely used 1RM estimator. The calculator above does this math instantly.
A hard set of 2 to 5 reps, taken close to failure with good form, gives the closest estimate. At 2 to 5 reps the published formulas agree within a few percent; past 10 to 12 reps they diverge, because you are measuring muscular endurance as much as strength. Use a weight you can lift 3 to 8 times for the best balance of safety and accuracy.
No. An estimate is a prediction fitted to typical lifter data; a tested max is a measurement. Your real max shifts with sleep, stress, technique, and fatigue. Train off the estimate and re-test rarely, ideally with a spotter. If you have actually tested a single, that tested number is your max.
Rarely, and never alone. A true single is a maximal effort with maximal consequences if technique breaks down: use a spotter or safety pins, warm up thoroughly, and do not test on a day you already feel beaten up. Most lifters get the same programming value from an estimated 1RM at a fraction of the risk.
Epley (1RM = weight × (1 + reps/30)) is the default here and has the broadest research support across the major lifts. Brzycki (weight × 36/(37 - reps)) is often closest at 10 reps or fewer and is popular for pressing. Lombardi (weight × reps⁰.10) sits near Epley at low reps. At low rep counts they agree closely, so keep test sets short rather than hunting for the right formula.
The calculator is unit-agnostic: enter the weight in kilograms or pounds and the result comes back in the same unit, because the formula only uses the ratio of reps to weight. Just stay consistent, and do not mix units between sessions you want to compare.
Roughly 8 reps. Per the Epley curve, 80% of 1RM corresponds to about 8 reps to failure. Useful landmarks: 85% is about 5 reps (strength work), 75% about 10 reps (hypertrophy volume), 71% about 12 reps, and 65% about 15 reps (muscular endurance).
Yes, with one caveat: deadlift estimates run slightly less accurate than squat or bench because deadlift strength drops off faster as fatigue accumulates. Use a 3 to 5 rep set for the most reliable deadlift estimate, and estimate each lift separately rather than carrying one number across exercises.
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