One Rep Max Calculator

What is One Rep Max (1RM)?

One Rep Max (1RM) is the maximum amount of weight you can lift for one repetition of a given exercise with proper form. It's a crucial metric for strength training as it helps determine appropriate training loads for different goals.

Rather than testing your 1RM directly (which can be risky and fatiguing), you can estimate it using mathematical formulas based on a weight you can lift for multiple repetitions. This calculator uses seven scientifically validated formulas to give you accurate 1RM estimates.

1RM Calculation Formulas

Epley (Most Popular)

The Epley formula (1985) is one of the most widely used and accurate formulas for estimating 1RM. It's particularly reliable for repetitions in the 1-10 range and is commonly used by strength coaches and athletes.

1RM = Weight × (1 + 0.0333 × Repetitions)

Brzycki

The Brzycki formula (1993) is another popular and accurate formula, especially for lower rep ranges (1-10 reps). It's commonly used in strength training programs and research.

1RM = Weight × 36 / (37 - Repetitions)

Lander

The Lander formula (1985) provides accurate estimates across a wide range of repetitions. It's known for being conservative and reliable.

1RM = (100 × Weight) / (101.3 - 2.67123 × Repetitions)

Lombardi

The Lombardi formula (1989) uses a power function (weight × reps^0.10) rather than a linear coefficient, which keeps it stable at higher rep counts where linear formulas overestimate. It is a good cross-check when you only have a moderate-rep set to work from.

1RM = Weight × Repetitions^0.10

Mayhew

The Mayhew formula (1992) was developed from bench press data and uses an exponential decay term. In the 2002 LeSuer validation it predicted the deadlift 1RM most accurately for the majority of subjects, making it a strong choice for posterior-chain lifts.

1RM = (100 × Weight) / (52.2 + 41.9 × e^{-0.055 × Repetitions})

O'Conner

The O'Conner formula (1989) is the simplest of the set (weight × (1 + 0.025 × reps)) and is the most conservative, returning slightly lower estimates than Epley. It is useful for beginners who want a cautious training-load baseline.

1RM = Weight × (1 + 0.025 × Repetitions)

Wathan

The Wathan formula (1994) also uses an exponential model and was the most accurate predictor of the bench press 1RM in the LeSuer study. It tends to track upper-body pressing strength better than the linear formulas.

1RM = (100 × Weight) / (48.8 + 53.8 × e^{-0.075 × Repetitions})

Training Zones & Rep Ranges

How to Use This Calculator

1. Perform an exercise (like bench press, squat, or deadlift) with a weight you can lift for multiple reps (ideally 3-10 reps)
2. Enter the weight you lifted and the number of repetitions completed
3. Choose a formula or use "Average of All Formulas" for the most balanced estimate
4. Review your estimated 1RM and training percentages
5. Use the training percentages table to plan your workouts based on your goals

Tips for Best Results

• Use a weight that challenges you but allows you to maintain proper form throughout all repetitions
• The most accurate estimates come from sets of 3-10 reps. Higher reps (15-20) are less accurate
• Always warm up properly before attempting heavy lifts
• For the most accurate results, test with reps between 3-8
• Different formulas may give slightly different results - using the average can provide a balanced estimate
• Re-test your 1RM estimate every 4-6 weeks as you get stronger
• Use training percentages to create periodized programs (varying intensity throughout your training cycle)
• For max strength (95-100%), rest 3-5 minutes between sets
• For hypertrophy (70-85%), rest 60-90 seconds between sets
• For endurance (60-70%), rest 30-60 seconds between sets

Important Safety Notes

• These formulas provide estimates - individual results may vary based on training experience and muscle fiber composition
• Never attempt a true 1RM test without proper warm-up and spotters
• Beginners should focus on learning proper form before testing or estimating 1RM
• The accuracy decreases significantly for reps above 15
• These calculations are most accurate for compound movements (squat, bench press, deadlift, overhead press)
• Always use proper form and never sacrifice technique for heavier weights
• If you're new to strength training, work with a qualified coach or trainer
• Listen to your body - if something doesn't feel right, stop immediately
• Progressive overload should be gradual - don't increase weights too quickly
• Adequate rest and nutrition are essential for strength gains and injury prevention

Which 1RM formula is the most accurate?

It depends on the lift and the rep range. The 2002 LeSuer study compared the most common formulas against actual measured 1RMs on bench, squat, and deadlift. Wathan came out best for the bench press, Lander best for the squat, and Mayhew best for the deadlift in most subjects, but all the modern formulas (Epley, Brzycki, Lombardi, Wathan, Lander, Mayhew, O'Conner) agree within about 2-5% of the true 1RM when reps are between 2 and 10. Above 10 reps the error grows rapidly because endurance and pacing dominate over pure strength. Epley is the most widely used because the math is simple (weight × reps × 0.0333 + weight). Picking any one formula and tracking it over time is more useful than chasing the "perfect" one - consistency matters more than the absolute number.

How do I convert RPE or reps-in-reserve (RIR) to a 1RM?

Set the RPE selector to match how hard the set actually was. Every formula here (Epley, Brzycki, etc.) assumes the entered reps were performed to true failure - but coaches, powerlifters, and programs like 5/3/1, RTS, and Sheiko almost never train compounds to failure. They log a load at a target RPE, for example 140 kg x 3 @ RPE 8 (2 reps in reserve). RPE 10 means 0 RIR (failure), RPE 9 means 1 RIR, RPE 8 means 2 RIR, and so on down to RPE 6 (4 RIR). This calculator uses the standard RTS / Tuchscherer RPE-to-%1RM chart: a (reps, RPE) pair maps directly to a percentage of your true 1RM, so a 3-rep set left at RPE 8 is treated as roughly an 86% load rather than a 3-rep max, correcting the estimate upward by about 6-8%. Leave it at RPE 10 if your set was a genuine all-out effort - the result is then identical to the classic failure-based formula.

How many reps give the most accurate 1RM estimate?

Three to five reps to failure. At 2-5 reps you're working at 87-95% of true 1RM, which is heavy enough that the formulas don't need to extrapolate far. At 1 rep there's nothing to estimate - that's already your 1RM. At 6-10 reps the estimates drift a few percent low because muscle fatigue and lactate accumulation start to limit reps before pure strength does. Above 10 reps the formulas become guesses (Brzycki literally breaks down at reps = 37). The sweet spot is 3-5 reps - heavy enough to be near-maximal, but with enough margin that you're not risking injury or grinding a true single. Most strength coaches recommend testing 1RM via a 3-5 RM rather than actual singles to reduce injury risk.

How often should I test or recalculate my 1RM?

For intermediate lifters, every 4-12 weeks depending on programming. Linear progression beginners (Starting Strength, Stronglifts) effectively retest every session because they add weight each workout. Once linear progression stalls, structured programs like 5/3/1 use a Training Max (about 90% of estimated 1RM) and retest every 3-4 mesocycle blocks (~12 weeks). Powerlifters peak for meets every 12-16 weeks. Testing more often than every 4 weeks rarely shows meaningful gains and adds CNS fatigue - the actual neural strength adaptation cycle is on the order of weeks, not days. Use formula estimates from heavy work sets between formal tests rather than maxing every week.

Why do my actual 1RM numbers differ from the calculator?

Several reasons. First, the formulas assume reps performed truly to failure with controlled tempo - if you grind reps with sloppy form or had reps in reserve, the estimate will be off. Second, rep efficiency varies by exercise: most lifters can do more reps at a given % of 1RM on lower-body lifts (squat, deadlift) than upper-body (bench, OHP), which is why squat estimates often come out 5-10% low. Third, CNS arousal at a true 1RM attempt is much higher than during multi-rep sets - some lifters add 5-10% in adrenaline alone. Fourth, individual physiology: fast-twitch lifters tend to outperform their estimated 1RM, endurance-types underperform. Track your personal ratio of actual-1RM to formula-1RM and apply it as a correction factor.

What's the difference between training percentages and 1RM percentages?

Training percentages are usually based on a Training Max (TM), which is intentionally set 5-10% below your true 1RM to enable consistent, repeatable workouts. Jim Wendler's 5/3/1 uses 90% of true 1RM as the TM and bases all working sets off it. The reasoning: a real 1RM can only be hit when fully rested with stimulants and adrenaline, but a training day at 80% of 1RM (which is really 89% of TM) needs to be doable on a Wednesday afternoon. So if a program prescribes "80% × 5 reps" it usually means 80% of TM, not 80% of true 1RM. This calculator shows percentages of 1RM directly - if you're following a TM-based program, multiply by 0.9 to convert.

Is testing 1RM safe for beginners?

Generally no, at least not in the first 6-12 months. True 1RM attempts require neuromuscular coordination and stabilizer strength that take months to develop, and bailing a failed squat or bench from a true max is the most dangerous moment in strength training. For beginners, almost everyone recommends estimating 1RM from a 3-5RM or even an 8-10RM and using that estimate to set training loads. Beginner programs (Starting Strength, GZCLP, Stronglifts 5x5) deliberately avoid 1RM testing for the first program cycle. Once you can squat your bodyweight, bench around 70% of bodyweight, and deadlift around 1.5× bodyweight with clean form, true maxing becomes lower-risk.

How do training percentages translate to muscle growth vs strength?

Strength adaptation is heaviest at 85-100% of 1RM (1-5 reps), where neural recruitment, rate coding, and intermuscular coordination dominate. Hypertrophy (muscle growth) peaks at 65-85% of 1RM (6-15 reps) where mechanical tension and metabolic stress are highest while still allowing enough total volume per session. Below 65% (15-30 reps) primarily trains muscular endurance and capillarization. Modern research (Brad Schoenfeld's volume meta-analyses) shows that hypertrophy responds primarily to total weekly volume regardless of rep range as long as sets are taken close to failure - so 10 sets of 5 reps and 5 sets of 10 reps with proximity to failure produce similar growth, with the lower-rep version building more strength alongside.

Can the calculator be used for accessory lifts and machines?

Yes, but with more error. The 1RM formulas were derived almost entirely from compound barbell lifts (bench, squat, deadlift), so accuracy on dumbbell curls, lateral raises, or cable rows is roughly 5-10% worse. Machine lifts compound the error because the path is fixed and stabilizers contribute less. For accessory work, most lifters don't actually need a 1RM - the appropriate intensity is determined by reps in reserve (RIR) or RPE (rate of perceived exertion), targeting 1-3 RIR for most working sets. Save 1RM testing for the compound lifts where loading precision actually matters for programming.