One Rep Max Calculator
Estimate your one-rep maximum (1RM) — the maximum weight you can lift for a single repetition — from a submaximal set using Epley, Brzycki, Lander, or other established formulas. Use it to design strength-training programs without the injury risk of testing actual maxes.
Last updated: May 2026
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About this calculator
The formula varies by selected method but all estimate 1RM from a known weight × reps performance. Epley formula: 1RM = weight × (1 + reps / 30). Brzycki: 1RM = weight × (36 / (37 − reps)). Lander: 1RM = (100 × weight) / (101.3 − 2.67123 × reps). Mayhew: 1RM = (100 × weight) / (52.2 + 41.9 × e^(−0.055 × reps)). All produce similar estimates in the 2-10 rep range, with progressively greater divergence at higher rep counts where accuracy degrades. Edge cases: 1 rep returns the input weight (formula returns near-identity); very high reps (15+) produce unreliable estimates because the predictive relationship between submaximal endurance and maximal strength weakens. For accurate 1RM estimation, use sets of 3-6 reps performed to true muscular failure. The formulas assume a standard relationship between reps and effort; technique varies between lifters (sticking points, bar speed at failure, etc.), making individual accuracy ±5-10% even with good test conditions. Brzycki tends to be most accurate at lower reps (2-5); Epley slightly overestimates at low reps and underestimates at high reps. Once you have an estimated 1RM, you can derive percentages: 90% 1RM (good for 3-4 reps), 80% (6-8 reps), 70% (10-12 reps), 60% (15+ reps). Most strength programs prescribe weights as percentages of 1RM (5/3/1 system, conjugate, Texas Method, etc.). For powerlifting and strength training specifically, knowing accurate 1RMs in squat, bench press, and deadlift is essential for program design; estimating 1RMs reduces the injury and recovery cost of actual max testing.
How to use
Example 1 — Epley estimation. You bench-press 100 kg for 5 reps to failure. Using Epley: 1RM = 100 × (1 + 5/30) = 100 × 1.167 = 116.7 kg. Enter 100 for Weight, 5 for Reps, "epley" for Formula. Result: 117 kg. ✓ A 100 kg × 5 reps submaximal set corresponds to roughly 117 kg max. This is the weight you could attempt for a single rep with good technique and proper warmup. Example 2 — Brzycki comparison. Same 100 kg × 5 set, using Brzycki: 1RM = 100 × (36 / (37 − 5)) = 100 × (36/32) = 112.5 kg. Brzycki produces 112.5 vs Epley's 116.7 — a 4.2 kg difference. ✓ Both estimates are in the 110-120 kg range; the true 1RM is likely around 113-117 kg. For programming purposes, use the more conservative estimate (Brzycki) when prescribing percentage-based loads to err on the safe side and ensure prescribed weights are actually liftable for the planned rep counts.
Frequently asked questions
Which 1RM formula is most accurate?
Brzycki tends to be most accurate at low reps (2-5), with error ±5-7% vs actual tested 1RM. Epley is slightly more accurate at moderate reps (5-10) but tends to overestimate at very low reps. Mayhew is good for moderate-high reps (8-12) but loses accuracy outside that range. For practical use, test using 3-6 reps to failure — that's the rep range where most formulas converge and give similar estimates. Truly maximal effort (failed rep, stopped just short) is essential; if you could have done one more rep, the formula underestimates true 1RM. Individual variation matters: some lifters have more rep capacity per pound than others (genetic predisposition toward type I muscle fibers, hypertrophy training history), which affects formula accuracy. For high-stakes programming (powerlifting meet preparation), prefer actual 1RM testing with experienced spotters over formula estimation.
When should I test my actual 1RM vs estimate?
Test actual 1RMs when: preparing for a powerlifting competition (need accurate openers); experienced lifter (3+ years training) with good technique and recovery capacity; using a competition-style format with proper spotters; have a 1-2 week deload planned to recover. Estimate 1RMs (don't test): when relatively new to lifting (under 1-2 years); when injury risk is a concern; during regular training cycles; when consistency in programming matters more than precise numbers. Most strength athletes test 1RM only 2-3 times per year (mid-program checks, contest prep openers, contest day); the rest of the time, they use estimated 1RMs from submaximal performance to design training. Frequent maxing is unnecessary and accumulates fatigue and injury risk without proportional benefit. For most lifters, a working 90% of estimated 1RM (a "training max") is the relevant number, not the calculated absolute max — programming around training max gives consistent intensity progression with less risk.
How does 1RM relate to strength training program design?
Most strength programs prescribe weights as percentages of 1RM. Common percentages and rep ranges: 90%+ 1RM = 1-3 reps (max strength training, powerlifting); 80-90% = 3-5 reps (strength); 70-80% = 6-10 reps (hypertrophy + strength); 60-70% = 10-15 reps (endurance); 50-60% = 15-25 reps (endurance/conditioning). Popular programs and their typical percentages: 5/3/1 uses 65-95% in cycles; Starting Strength uses linear progression from ~70-90%; conjugate method (Westside Barbell) varies 50-90%+ depending on the day; Texas Method uses 70-90% across the week. Knowing your current 1RM in major lifts (squat, bench, deadlift) enables you to: prescribe appropriate weights at each session; track progress (1RM should rise with training); manage fatigue (avoid going to failure too often or with too-heavy weight). Update estimated 1RMs every 6-12 weeks during training cycles to keep programming aligned with current strength.
What are the most common mistakes people make with 1RM?
The biggest is calculating 1RM from sets that weren't actually to failure — if you stopped with reps in reserve, the formula underestimates true 1RM by 5-15%. The second is using high-rep sets (15+) to estimate 1RM; the predictive relationship weakens at high reps because endurance and maximum strength are partially independent qualities. The third is testing actual 1RMs too frequently; this accumulates fatigue and injury risk without proportional benefit. The fourth is comparing 1RMs across different lift variations (high-bar squat vs low-bar squat, conventional vs sumo deadlift) — these are different exercises with different leverage; track each separately. The fifth is chasing 1RM numbers at the expense of technique; ego-driven 1RM attempts often involve compromised form that increases injury risk and produces unreliable estimates. The sixth is using estimated 1RM from one lift to predict another; bench press 1RM tells you nothing about squat or deadlift 1RM. The seventh is not deloading before 1RM test attempts; fatigue from prior heavy training easily reduces 1RM by 10-15%.
When should I not use this calculator?
Skip it for new lifters (under 6 months of consistent training) who haven't developed neural efficiency to express maximum strength — formulas underestimate trained-lifter 1RMs and overestimate novice 1RMs. It is the wrong tool for olympic lifts (clean and jerk, snatch) where technique-specific factors dominate strength; use lift-specific assessment. Do not use it for very high rep work (over 20 reps); the predictive relationship breaks down and the result is meaningless. For elderly lifters, those recovering from injury, or anyone with cardiovascular concerns, 1RM estimation is safer than actual testing — but don't use either to design extreme programs without medical clearance. For powerlifting competition openers specifically, actual recent 1RMs are essential; formulas estimate but don't replace tested performance. And for tactical/military fitness testing requirements, follow the specific protocols required by your organization rather than substituting calculator estimates.