One Rep Max Calculator for Weightlifting
Your one rep max, the heaviest weight you can lift for one clean rep, is the number every serious training program is built on. Percentages of it set your working weights, your progression, and whether a session targets maximal strength, muscle size or endurance. But a true 1RM test is risky business: it asks for perfect form under maximal load, a spotter, and a fully recovered body, and if any of those are missing, the test can become the injury. This one rep max calculator for weightlifting hands you the number without the danger. Type in a weight you lifted recently and the clean reps you managed, and it estimates your 1RM with four of the most validated formulas in strength science. Epley, Brzycki, Lombardi and O'Conner, then averages them into a single figure. You also get a percentage table from 95% down to 60%, so you can walk into your next session knowing exactly what goes on the bar. Bench press, squat, deadlift, overhead press, any barbell or dumbbell lift, in kilograms or pounds.
Last updated: October 22, 2026
Your result
Estimates only, never attempt a true one rep max without a spotter and safety bars.
The formula
Epley: 1RM = weight × (1 + reps ÷ 30)Brzycki: 1RM = weight × 36 ÷ (37 − reps)Lombardi: 1RM = weight × reps^0.10O’Conner: 1RM = weight × (1 + reps ÷ 40)Estimated 1RM = average of the four formula resultsTraining weight = estimated 1RM × target percentage
A worked example
Lift 100 kg for 5 clean reps: Epley gives 116.7 kg, Brzycki 112.5 kg, Lombardi 117.5 kg and O’Conner 112.5 kg, an average estimate of about 115 kg. Your 90% training weight would then be roughly 103 kg.
More about the One Rep Max Calculator
What a one rep max actually measures
A one rep max is the heaviest load you can move through a full range of motion exactly once, with clean form. It captures maximal force production, muscle size, neural drive, technique and even nerve, all blended, for one specific lift. Your bench 1RM says nothing about your squat; every lift carries its own number.
Programs revolve around it because percentages of 1RM are the most reliable way to set intensity. Telling two lifters to "go heavy" means nothing; putting both at 85% of their 1RM gives each the same relative challenge. An honest estimate beats a brave guess, every time.
The four formulas, and why they disagree
Epley (1985) assumes every extra rep costs a fixed slice of your max, simple, and slightly generous. Brzycki runs a touch more conservative, which is why coaches like it. Lombardi follows an exponential curve that fits experienced lifters well. O'Conner is the most cautious of the four, the one to trust when you would rather undershoot than overshoot.
They disagree because each was built from a different crowd of lifters doing different lifts. No single equation is "true", which is exactly why this calculator shows all four and averages them. The average holds steadier than any lone formula, especially in the 3 to 8 rep sweet spot.
How many reps to enter for the best estimate
Feed it a recent set taken close to failure with good form, 3 to 8 reps is the sweet spot. There, all four formulas converge and the estimate is at its most trustworthy. A single rep needs no estimating, and two reps work but leave the math thin.
Skip high rep sets. Past about 10 reps, muscular endurance starts contaminating the numbers and every formula drifts upward, sometimes badly. A grinding set of 15 measures stamina, not maximal strength. Go heavier, do fewer reps, and retest.
Reading the percentage table
The table under your result turns the estimate into a plan. As a rough map: 90 to 100% of 1RM is maximal strength territory (1 to 3 reps a set), 80 to 90% builds strength with a side of size, 70 to 85% is the classic hypertrophy zone, and 60 to 70% suits endurance, technique work and warm ups.
Pick the zone that fits your goal and load the listed weight. If 85% feels impossibly heavy that day, treat it as information, you are probably under recovered, not as a dare to force out reps your body cannot safely finish.
Where the estimates break down
Beginners get the noisiest numbers. Early progress is mostly motor learning, so a shaky five reps undersells what the muscles could do once technique settles. As a novice, re estimate every few weeks and enjoy watching the number climb.
Form outranks math here. Bounced reps, half range of motion, or a spotter's fingers sneaking under the bar all inflate the input, and the estimate with it. Only clean, unassisted reps belong in the calculator. Garbage in, PR out is not how this works.
If you ever test a true 1RM, do it safely
An estimate keeps you safe precisely because a genuine max attempt is the riskiest set in the gym. If you do test for real, use a spotter you trust plus safety bars or pins, warm up in small jumps, and rest fully between attempts, three to five minutes, not ninety seconds.
Never max out sick, injured or running on empty, and never chase a missed lift with an instant retry at the same weight. One sensible test per lift every couple of months is plenty. The rest of the time, let the calculator and the percentage table do the heavy thinking for you.
How to use the One Rep Max Calculator
- Pick your units, kilograms or pounds.
- Enter the weight you lifted and the clean reps you completed (1 to 12).
- Hit Calculate to see your estimated 1RM, the average of four proven formulas.
- Use the percentage table to choose working weights for your next session.
Frequently asked questions
How accurate is a 1RM calculator?
Very good, given the right input: a 3 to 8 rep set taken near failure with clean form usually lands within about 5% of a true tested max. Accuracy slides with high rep sets, sloppy reps, or beginners whose technique is still the limiting factor. Trustworthy estimate, yes, laboratory measurement, no.
Which 1RM formula is the most accurate?
No single formula wins outright, Epley leans generous, Brzycki and O'Conner lean conservative, Lombardi suits experienced lifters. The research keeps landing in the same place: averaging several validated formulas beats trusting any one of them, which is exactly what this calculator does.
How many reps should I enter for the best estimate?
Three to eight clean reps, taken close to failure. That is where all four formulas agree most. Anything over 10 reps starts measuring endurance instead of maximal strength, and every formula drifts high.
Can I use this for bench press, squat and deadlift?
Any barbell or dumbbell lift works, bench press, squat, deadlift, overhead press, rows and more. One caveat: the estimate is lift specific, so run each lift separately instead of assuming ratios between them.
How do I use the percentage table in my training?
Match the percentage to your goal, 90 to 100% for maximal strength (1 to 3 reps), 80 to 90% for strength with size, 70 to 85% for hypertrophy, 60 to 70% for endurance and technique. Load the listed weight for your working sets, then nudge it up as the sets start feeling easy.
Why do the four formulas give different numbers?
Each was built from a different group of lifters, so each bakes in its own assumption about how quickly strength fades per rep. The spread is normal, and usually small in the 3 to 8 range. The four way average is steadier than any single formula.
Does this work in pounds as well as kilograms?
Flip the units toggle to Imperial and enter pounds, every result, percentage table included, comes back in pounds. The math does not care about units; only the label changes.
What is the difference between my one rep max and my training max?
Your one rep max is your estimated ceiling; your training max is a slightly reduced number, many programs set it around 90% of your 1RM. That your working weights are calculated from. It builds in a buffer for tired days and keeps progress moving for longer. Use the percentage table above to set your training max, then plan your sessions off that instead of the raw estimate.
How do I calculate my one rep max?
Use the Epley formula: 1RM = weight lifted × (1 + reps ÷ 30). For example, benching 100 kg for 8 reps estimates a 1RM of 100 × (1 + 8/30) = 127 kg. It is most accurate with sets of 3 to 10 reps, always test your true max with a spotter.
What is a one rep max and why does it matter?
Your one rep max (1RM) is the heaviest weight you can lift for a single repetition of an exercise like the bench press or squat. Training programs use percentages of your 1RM to set working weights, for example 5 sets of 5 reps at 80% of 1RM. You can estimate it from a lighter set taken near failure instead of risking a true max attempt.