One Rep Max Calculator
Estimate your 1RM using 7 proven strength formulas
This 1RM calculator estimates your one-rep max from a submaximal lift, using seven validated formulas (Epley, Brzycki, Lombardi, Mayhew, O'Conner, Wathan, Lander) and averaging the results. Enter the weight you used and the number of clean reps to failure, and the calculator returns your estimated 1RM in kg or lbs, plus a complete percentage chart for programming.
This matters because testing an actual 1RM under the bar is risky if your technique fluctuates or you train alone. The formulas were built precisely so coaches and athletes could program at percentage-based intensities (75%, 80%, 85% of 1RM) without anyone needing to test absolute max weekly. Epley (the most cited) is accurate within roughly 5 to 8% in the 3 to 10 rep range; accuracy drops above 10 reps.
Built and reviewed by Kazi Habib, B.Pharm, MBA, PMP. The deep dive below covers which formula fits which exercise (Brzycki tends to undercall on big compounds, Epley overcalls on isolation work), how to use the percentage chart for actual programming, and the safety note nobody puts above the calculator: do not test a true 1RM without a spotter or safety pins.
Between 1 and 30 reps
How this calculator works
The seven formulas each estimate 1RM from weight and reps using slightly different equations. The most common: Epley (1RM = weight x (1 + reps/30)), Brzycki (1RM = weight x 36 / (37 - reps)), and Lombardi (1RM = weight x reps^0.10). Each was validated against test populations in lab settings, generally for the 1 to 10 rep range. Past 10 reps, all of them lose accuracy because endurance and technique drift dominate the rep count rather than absolute strength.
The calculator runs all seven and shows an average. It then maps that 1RM to the standard percentage chart (60% to 100% in 5% increments) with associated rep ranges so you can program directly.
When to use this calculator
Use this when you finished a top set in your training log and want to know your current 1RM without testing, when you are starting a percentage-based program (5/3/1, Smolov, Hatch) and need your starting 1RM, when your gym does not allow you to test true 1RMs alone (most commercial gyms in Canada have this rule), or when you are returning from a layoff and want a target before building back up.
When NOT to use this calculator
Skip this if the weight you entered is for a set above 10 reps. The formulas degrade fast past that. Re-do at a heavier weight that you can only get for 3 to 8 reps. If the exercise was an isolation movement (bicep curl, leg extension), the formulas were validated on compound lifts; isolation 1RM estimates are mostly fiction. Machine 1RMs are not directly comparable across machines and the formula assumptions break down. If you did not lift to genuine failure (stopped with 2 reps in reserve), the estimate undercalls your real 1RM by a meaningful margin.
What the result actually means
The estimated 1RM is your projected maximum for one clean rep with full ROM under typical fatigue and technique conditions. The seven-formula average reduces the bias of any single equation; if you compare formulas, Epley tends to read 2 to 4% higher than Brzycki for the same input, and the truth usually sits between them.
For programming: use 80 to 85% for hypertrophy work (5 to 8 reps), 85 to 90% for strength work (3 to 5 reps), 90%+ only when peaking. The percentage chart on this page maps reps to percentages for direct programming. Do not chase 95%+ work weekly; the systemic fatigue accumulates faster than the strength gain, and most strength research supports peaking only every 4 to 12 weeks.
Pharmacist take
Strength testing intersects with several medication classes. Beta-blockers (propranolol, metoprolol) blunt the heart rate response to max effort and can affect perceived exertion; the formula still works but the lift feels different. Statins occasionally cause muscle weakness or pain that fluctuates day to day; an unexplained 1RM drop in someone newly on a statin warrants a CK test and a conversation with the prescriber. Anyone on anticoagulants (warfarin, apixaban) needs to think carefully about Valsalva maneuver risks at near-max loads, particularly with squat and deadlift.
Halal, Canadian, and dietary considerations
Halal pre-workout for strength training is a legitimate question because most North American pre-workouts use ethanol-extracted natural flavours and sometimes gelatin capsules. For Canadian gyms, GoodLife and Fit4Less have national reach with safety pin racks; Iron Strong Gym (Mississauga), Strength Lab (Calgary), and most CrossFit affiliates have proper safety setups for legitimate 1RM testing if you decide to verify the estimate.
Methodology and sources
The seven formulas are documented strength assessment equations published in physical education and strength training literature dating to Epley (1985) and Brzycki (1993). The percentage chart and rep-range mapping reflect the National Strength and Conditioning Association programming framework, which has been the standard reference for strength coaches since the 1990s. The 10-rep ceiling for accuracy is a documented limitation of all submaximal estimation methods. See also the American College of Sports Medicine physical activity guidelines for context on weekly strength training recommendations.
Using Your 1RM to Structure Smarter Training
Your one-rep max (1RM) is the heaviest weight you can lift for a single repetition with proper form. Beyond being a bragging right, it's the reference number that makes structured strength programming possible — every percentage-based program (5/3/1, Starting Strength, Greyskull LP, most powerlifting templates) depends on knowing your 1RM.
For most trainees, testing a true 1RM isn't worth the injury risk and recovery cost. Estimating it from submaximal work is safer and nearly as accurate. The Epley and Brzycki formulas use your reps at a given weight to predict your 1RM within 3-5% for most people in the 3-10 rep range. Accuracy drops above 10 reps — high-rep max attempts tell you more about muscular endurance than true strength. If you bench 225 lbs for 5 clean reps, your estimated 1RM is roughly 260 lbs.
Knowing your 1RM unlocks percentage-based training. Hypertrophy work lives at 65-80% of 1RM for 6-12 reps. Strength work uses 80-92% for 3-6 reps. Peaking work pushes above 92%. The scientific literature (Schoenfeld et al., 2017) shows that hitting a minimum weekly volume at appropriate intensities drives progress — not maximum effort every set. A 1RM gives you the anchor for applying these principles.
Re-test every 8-12 weeks. Newer lifters gain quickly — a 1RM from 3 months ago is often already outdated. Intermediate and advanced lifters progress slower, so longer re-test windows are fine. Use your estimated 1RM to program your next training block, track progressive overload, and spot plateaus early. When three consecutive blocks show no 1RM increase despite consistent training, it's time to change variables: exercise selection, volume, or recovery protocols.
Keep learning
- →One-Rep Max Guide for Strength TrainingFull guide to testing, estimating, and applying your 1RM.
- →Progressive Overload ExplainedThe principle that drives every 1RM increase.
- →Strength Training Beginner's GuideStarting from zero? Begin here.
- →Best Creatine Monohydrate 2026The single best-studied supplement for increasing 1RM.
One-Rep Max FAQ
Your one-rep max is the maximum weight you can lift for a single repetition with proper form. It is used to program training intensities — for example, working at 70-85% of your 1RM for hypertrophy or 85-95% for strength.
Testing a true 1RM carries higher injury risk, especially for beginners. Using an estimated 1RM calculated from a sub-maximal set (e.g., 5 reps at a given weight) is safer and nearly as accurate. Save true 1RM testing for competition prep or after several months of consistent training.
No single formula is universally best. The Epley and Brzycki formulas are most widely used and tend to be accurate for sets of 1-10 reps. Accuracy decreases with higher rep counts (15+). Our calculator uses multiple formulas and shows the average for the most reliable estimate.
Recalculate every 4-6 weeks or whenever you notice your working weights have changed significantly. Strength improves with training, and your percentages should update accordingly to continue progressing.