What this calculator does
Estimate the most weight you could lift once, without having to try it. That number is your one-rep max (1RM): the heaviest weight you can lift one time with good form on a given exercise. Testing it for real means an all-out attempt, which is tiring and riskier than normal training.
So most lifters estimate it from a lighter set instead. That's a weight they lifted for several reps, taken close to failure (the point where you couldn't do one more good rep).
This calculator uses seven published prediction formulas, each named after the researchers who proposed it. You pick which one leads. You'll see every formula side by side, their average, and a table of weights from 50% to 100% of your estimate for planning sets.
The result is an estimate, not a guarantee, and it isn't medical advice. Lift with a spotter or safety equipment. If you have any health concerns, see a doctor before starting hard training.
Where it's used
Why this math matters outside the classroom:
- Epley formula. Lifting 185 lb for 5 reps gives an Epley estimate of 185 × (1 + 5 ÷ 30), which is about 215.8 lb.
- Training percentages. A program set at 80% of a 215 lb max puts about 172 lb on the bar for those sets.
- Comparing equations. Coaches compare Epley and Brzycki on the same set and find they match at 10 reps but drift apart at higher counts.
- Tracking strength. Lifters log estimated maxes from regular working sets to see progress without testing a true single.
- Team testing. Strength coaches estimate maxes for a whole team from rep sets, which takes less time than testing every athlete's single.
Grade level and standards: Grades 6–7; Common Core State Standards for Mathematics 6.EE.A.2.c, 6.RP.A.3.c. © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved.
How to use it
- Enter the weight you lifted and choose pounds or kilograms.
- Enter how many reps you finished with good form, from 1 to 12.
- Choose a formula. Epley is the default, and the others are shown in the results for comparison.
- Use the percentage table to pick working weights for your program.
What the inputs mean
- Reps completed
- Use a set you took close to failure. A set you stopped well short of failure makes the estimate too low. The formulas are most reliable for 10 reps or fewer. Above 10, the calculator still gives an estimate but adds a warning.
- Formula
- The formulas agree closely at low reps and drift apart as reps go up. None is best for everyone or every exercise.
Formula and method
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) Lander: 1RM = 100 × w ÷ (101.3 − 2.67123 × r) Mayhew: 1RM = 100 × w ÷ (52.2 + 41.9 × e^(−0.055 × r)) Wathan: 1RM = 100 × w ÷ (48.8 + 53.8 × e^(−0.075 × r))
In every formula, w is the weight you lifted and r is the number of reps. In two formulas, e is a fixed math constant, about 2.718. The answer comes out in the same unit you entered, so there's nothing to convert.
If you enter a single rep, the calculator gives back the weight itself, because a one-rep set already is a one-rep max.
The training table multiplies your chosen estimate by 100%, 95%, 90% and so on, down to 50%.
Worked example
A lifter bench-presses 185 lb for 5 reps and uses the Epley formula.
- Epley: 185 × (1 + 5 ÷ 30) = 185 × 1.1667 = 215.83 lb.
- The other formulas range from 208.13 lb (Brzycki and O'Conner) to 220.17 lb (Mayhew), with an average of 213.66 lb.
- A working weight at 80% is 215.83 × 0.8 = 172.67 lb.
Result: The estimated one-rep max is about 215.8 lb. So sets at 80% would use roughly 172.7 lb.
Understanding the result
Expect your true 1RM to land somewhere in the range the formulas give, not on one exact number. The range is narrow at 3 to 5 reps and gets wider beyond 10.
Estimates tend to be more accurate for experienced lifters than for beginners. They're also better for big multi-joint lifts, such as the squat, bench press and deadlift, than for single-muscle exercises like curls.
Use the table as a starting point. If a planned percentage feels far too easy or too hard, adjust based on how your sets really go.
Assumptions and limitations
- The set was done with steady technique and taken close to failure.
- The link between reps and weight follows the formula you chose.
- A single rep is treated as a real one-rep max.
- Estimates beyond 10 reps are less reliable, and the calculator doesn't accept more than 12.
- Tiredness, sleep, warm-up and technique all affect how you perform on the day.
- The formulas were developed on particular groups of lifters and exercises, so they may not suit everyone.
Frequently asked questions
Which one-rep max formula is the most accurate?
No single formula wins in every study. Epley and Brzycki are the most widely used, and they give identical answers at 10 reps. Looking at the range across all seven gives you a feel for the uncertainty.
Why are high-rep sets less reliable?
Sets of many reps depend more on muscle endurance than on top strength, and endurance varies a lot from person to person. Two people who can each do 15 reps with the same weight can have quite different maxes.
Should I test my true one-rep max?
Many people never need to. An estimate from a heavy set of 3 to 5 reps is enough to plan your training. If you do test, warm up well and use a spotter or safety bars.
Does it matter whether I enter pounds or kilograms?
No. The formulas work in any unit, and the answer and table use the unit you chose.
How this calculator is checked
Method: Published one-rep-max prediction equations of Epley, Brzycki, Lombardi, O'Conner, Lander, Mayhew and Wathan, as commonly stated in strength-training literature. The calculation is covered by automated tests with known reference values and edge cases. Last updated 2026-10-18. Found a problem? Tell us.
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