One Rep Max Calculator: Estimate Your 1RM Safely (Free)
Type the weight and reps from any hard set. The calculator averages the Brzycki and Epley formulas and lays out the working weights below it.
Estimated one-rep max
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| % | Weight lifted | Reps at this weight |
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Quick answer
A one-rep max calculator estimates the heaviest weight you could lift once from a set you actually did. Enter the weight and the reps (1 to 15); the tool runs the Brzycki formula (weight ÷ (1.0278 − 0.0278 × reps)) and the Epley formula (weight × (1 + reps ÷ 30)) and shows the average. From 2 to 10 reps the estimate usually lands within 5 to 10 percent of a tested max. Above 10 reps it drifts, which is why the calculator stops at 15.
This calculator runs entirely in your browser: nothing you type is uploaded, stored or sent anywhere, and it keeps working with the connection off. Enter a weight and a rep count from a set you have actually done, and it estimates the heaviest weight you could lift for a single clean rep. Percentage charts and most strength programs are written against that number, so it helps to know where it comes from.
How to use it
Start with a recent hard set. The estimate is only as good as the set behind it, so use one taken to within a rep or two of failure, with form you would accept on a max attempt. Sets of 2 to 8 reps give the most reliable answer; a set of 5 is the classic input.
Type the total load, bar included. A standard Olympic bar is 20 kg or 45 lb, and leaving it out shifts every number on the page by the same amount. Switch the unit to kg or lb so the table reads in the plates you actually load.
Then type the reps you completed, from 1 to 15. Type more than 15 and the field snaps back to 15, for reasons covered below.
The large figure is your estimated one-rep max, rounded to the nearest half unit. The smaller line under it shows the two formulas the average came from, so you can see how far apart they are for your particular set. Each row of the percentage table gives a working weight at a percentage of the estimate, next to a typical rep count at that load. Plan a session from it, or check whether the weight your program prescribes is realistic for you this week.
If you enter 1 rep, the calculator tells you plainly that a true single needs no estimate. The number you lifted is the number.
What estimated 1RM means here
An estimated one-rep max, often written e1RM, is a projection: given that you lifted this weight for this many reps, here is the single-rep load that effort corresponds to. Two published formulas do the projection in this tool.
Matt Brzycki fitted a straight line to the relationship between reps and percentage of max, published in 1993 in the Journal of Physical Education, Recreation and Dance:
1RM = weight ÷ (1.0278 − 0.0278 × reps)
At 1 rep the divisor is exactly 1, so a single returns itself. Each extra rep removes 2.78 percent from the divisor, which is why the formula climbs faster and faster as reps rise.
Boyd Epley's formula came from a University of Nebraska poundage chart rather than a journal, but it has been validated many times since:
1RM = weight × (1 + reps ÷ 30)
Each rep adds a flat 3.33 percent. It is linear, which makes it easy to run in your head: 100 kg for 6 reps is 100 × 1.2, or 120 kg.
Why average them? Take 80 kg for 5 reps. Brzycki gives 90.0 kg, Epley gives 93.3 kg, and the calculator shows 91.5 kg. Across the useful range the two bracket the truth from opposite sides: Brzycki sits a touch low for very low rep counts and high for long sets, while Epley does the reverse. Around 10 reps they cross; 100 kg for 10 reps is 133.4 kg by Brzycki and 133.3 kg by Epley. Averaging cancels most of each formula's bias without inventing a third equation, and the line under the result keeps both original numbers visible.
One wrinkle. Because Epley adds 3.33 percent even at one rep, an entry of 1 rep shows an average slightly above the weight you typed. The calculator flags this as a true single; treat the bar weight as your max and ignore the rounding.
The 15-rep ceiling has a reason too. Both formulas were fitted to sets in the low-to-moderate rep range, and they disagree more the further you leave it. At 15 reps, 100 kg is 163.7 kg by Brzycki and 150 kg by Epley, a 9 percent gap. At 20 reps the gap is wider, and the set itself has become a test of endurance and pain tolerance more than of maximal force. Rather than show a number with a wide error bar as if it were precise, the calculator stops at 15 and asks you to use a heavier set.
How accurate is it
Close enough to program from. Not close enough to bet a competition on.
LeSuer and colleagues compared seven prediction equations across bench, squat and deadlift in 1997, and found correlations above 0.95 between predicted and tested maxes, with average errors of a few kilograms in the 2 to 10 rep range. Expect your own estimate to land within 5 to 10 percent of what you could actually lift. Four things move it around.
The lift is the biggest one. Bench press and squat estimates are the tightest. Deadlift estimates tend to run low, because grip and back fatigue end a deadlift set before the prime movers are truly done, so the rep count understates your single.
Training age matters too. Experienced lifters are more efficient at low reps and get more reps at a given percentage than beginners, so the formulas fit them differently. A lifter in their first year often tests below the estimate; a lifter with five years under the bar sometimes tests above it.
Then the rep count. The sweet spot is 2 to 8. From 8 to 10 the error widens slightly; above 10 it widens quickly, and by 15 the two formulas are 9 percent apart before you account for the day, the sleep and the coffee.
And the set itself. A set stopped three reps short of failure will underestimate. A set with a bounced last rep will overestimate. The same effort level every time produces a trend you can trust.
Any single estimate carries that noise. A sequence of estimates from similar sets over several weeks carries much less, because the noise averages out while the signal, whether you are getting stronger, accumulates. That is why an estimated max is a better tracking tool than a tested one, even though a tested one is more accurate on the day.
Percentage of 1RM: what the table means
The table under the calculator uses the same rows every time; only the weights change. Here is what each row is for.
| % of 1RM | Typical reps | What it is used for |
|---|---|---|
| 100% | 1 | A max attempt; only after a proper warm-up ladder |
| 95% | 2 | Heavy doubles; peaking blocks |
| 90% | 4 | Heavy strength work; top sets in a 5/3/1-style week |
| 85% | 6 | Classic strength sets: 5×5, 4×6 |
| 80% | 8 | Strength with some hypertrophy; 3×8, 4×8 |
| 75% | 10 | Hypertrophy range; 3×10 |
| 70% | 12 | Higher-rep hypertrophy; 3×12 |
| 65% | 15 | Endurance and technique work |
Read across for a session. If your estimated squat is 140 kg and the program says 3 sets of 8, the table hands you 112 kg. If it says 5×5 at 85 percent, that is 119 kg, and you round to the plates you have. The rep column also tells you whether the prescription is sane: 3×8 at 90 percent is a missed set waiting to happen.
The rep-at-percentage figures are averages. Lifters with a lot of fast-twitch muscle get fewer reps at 80 percent; lifters built for endurance get more. If you consistently get 10 reps where the table says 8, your true max is a little higher than the estimate, or you are simply a high-rep responder. Either way, use your own numbers once you have them. The full chart, with more percentage steps and worked examples, is in the 1RM percentage chart.
When not to test a true max
The calculator exists so that you rarely have to load a bar to the limit. Five situations where testing is the wrong call.
Under about six months on a movement, your form is still changing, and a max attempt tests the weakest link in a chain you have not yet built. Estimates from sets of 5 to 8 are safer and, at this stage, just as informative.
Tired, unwell or short on sleep. A max is a snapshot of your nervous system on the day. On a bad day it tells you about the day.
A niggle. Anything that is already sore under submaximal load will not enjoy 100 percent. Estimate instead, and let the trend tell you when things have settled.
No spotter and no safeties. Bench press and squat maxes belong in a rack with the pins set, with a spotter who knows the plan. Without both, stay with heavy triples.
The middle of a training block. Testing costs a session and a couple of days of recovery. Unless the block is designed to end in a test, the estimate from your top set already tells you what you need.
When a test is worth doing, and how to run the warm-up ladder so it goes well, is the subject of how to test your one rep max safely.
The other tools
Once you have an estimate, two more calculators finish the job. The plate calculator turns a target weight into the plates to load on each side, so 119 kg becomes a bar, two 20s, a 10 and a 2.5 without arithmetic between sets. The training volume calculator sums weight times reps across a session or a week, which tells you whether the workload behind your estimated max is rising, steady or slipping.
Where to go next
A calculator gives you one number, once. The reason to track the number is to watch it move, and that needs a log that keeps the history.
Strongbro computes an estimated one-rep max from every set you log, keeps the best per exercise, and marks the day it changed. The personal records feature covers what gets tracked and how the monthly records view reads. Insights charts e1RM alongside weekly volume and per-muscle split, so a flat max can be traced back to a volume dip or a missed session rather than guessed at.
If you want the logic before the software, how to track personal bests in the gym covers weight-at-reps records and why an estimated max ties them together. The estimate is only a scoreboard, though. How to apply progressive overload walks through when to add weight, when to add reps, and how to use the percentage table to plan the next increment.
What to take to the rack
Enter a hard set of 2 to 10 reps, bar weight included, and you get an estimated one-rep max averaged from the Brzycki and Epley formulas, along with the working weights at every common percentage. Expect it to sit within 5 to 10 percent of a tested max, tighter on bench and squat, looser on deadlift and above 10 reps. Use the estimate to set training weights and to watch your strength trend from week to week. Save the true test for the few days a year when a real number matters and the rack, the spotter and the warm-up are all in place.
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Frequently asked questions
Which formula does this one-rep max calculator use?
Two, averaged. Brzycki divides the weight by (1.0278 − 0.0278 × reps). Epley multiplies the weight by (1 + reps ÷ 30). Between 2 and 10 reps they agree within a few percent; averaging them smooths out the small bias each one has at the low and high ends of that range.
How accurate is an estimated one-rep max?
For sets of 2 to 10 reps, expect it within 5 to 10 percent of a tested max. LeSuer and colleagues found correlations above 0.95 between predicted and tested maxes in that range. The estimate is tighter on bench press and squat than on deadlift. Above 10 reps the formulas diverge and the error grows quickly.
Why does the calculator stop at 15 reps?
Because past that point you are measuring muscular endurance, not maximal strength. At 15 reps Brzycki and Epley already disagree by about 9 percent, and at 20 reps the gap is wider still. Sets above 15 tell you something useful about your conditioning, but not much about your max.
Should I enter the bar weight?
Yes. Enter the total load you moved: plates plus bar. A standard Olympic bar weighs 20 kg (45 lb), and the difference matters. If you type only the plates, the estimate and every row of the percentage table will be off by the same 20 kg.
What counts as a rep for this calculation?
A full-range rep with the form you would accept on a max attempt. Half squats and bounced bench reps inflate the count and the estimate with it. If the last rep was ugly, do not count it; the formulas assume the set stopped where technique still held.
Is estimated 1RM the same as a tested 1RM?
No. A tested max is a lift you actually made. An estimate is a projection from a submaximal set. Estimates are safer, faster and repeatable every week, which makes them better for tracking. A tested max is the only true answer for a competition or a specific number you want to claim.
Can I use this for dumbbells and machines?
You can, with a caveat. The formulas were built on barbell lifts. Dumbbell pressing and machine work tend to fatigue differently, so the estimate is rougher. It is still useful for setting working weights from week to week, as long as you compare like with like.
Why does the result differ from another calculator I used?
Different sites pick different formulas. Some use Brzycki alone, some Epley, some Lombardi or O'Conner. At 5 reps the spread across them is a few percent; at 12 reps it can be 10 percent. This tool shows both of its inputs under the result so you can see where the average came from.
How often should I recalculate my 1RM?
Whenever you do a hard set. In practice that means a fresh estimate most weeks on each main lift. Watch the trend over a month rather than reacting to one number; a poor night's sleep can move a single estimate by 5 percent without anything real having changed.
Does Strongbro do this automatically?
Yes. Every set you log is scored with the same kind of formula, and the app keeps an estimated one-rep max per exercise, checks each set against your history for records, and charts the trend. The calculator here is the same idea for people who want a single number without an account.
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