Enter a weight and the number of reps you completed with it, and this calculator estimates your one rep max using the Epley and Brzycki formulas, then builds the full percentage chart underneath — rounded to weights you can actually load on a barbell. It runs entirely in your browser, and nothing you type is sent anywhere.
| % of max | Load | Approx. reps |
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What a one rep max actually is
Your one rep max, usually written as 1RM, is the heaviest weight you can lift for a single complete repetition of an exercise with sound technique. It is the standard reference point in strength programming, because once you know it, every other load in a program can be expressed as a percentage of it.
Most people never test a true max, and there are good reasons for that. Testing is fatiguing, it carries more injury risk than ordinary training, and on lifts like the squat and bench press it needs a spotter or safety bars to attempt honestly. So the common approach is to take a set you already performed, feed the weight and rep count into a formula, and program from the estimate. That is what this calculator does.
The formulas this calculator uses
Two estimation formulas dominate strength training, and this tool shows both rather than hiding the disagreement between them.
Epley (Boyd Epley, 1985) multiplies the weight by one plus the reps divided by thirty. Brzycki (Matt Brzycki, published in JOPERD in 1993) multiplies the weight by thirty-six divided by thirty-seven minus the reps.
They agree closely at low rep counts and drift apart as reps climb, and they swap places on the way. Below ten reps Epley returns the higher figure. At exactly ten reps the two formulas produce an identical result. Above ten reps Brzycki returns the higher figure. The headline number above is the average of the two. That is a deliberate editorial choice rather than a validated method: when two reasonable formulas disagree, splitting them is more defensible than picking a favourite. Both individual values are shown so you can use whichever your program specifies.
How to use the percentage chart
Once you have an estimated max, percentages give you working loads. A program that calls for three sets of five at eighty percent is telling you to find the eighty percent row and load that weight. The blue band in the chart marks roughly seventy to ninety percent, which is where most strength and hypertrophy work lives — heavy enough to drive adaptation, light enough to accumulate meaningful volume.
Loads are rounded to the nearest five pounds or two and a half kilos, because a barbell can only be loaded in real plate increments. A calculated 237.4 pounds is not something you can put on a bar. The exact figure sits underneath each rounded load in smaller text if your gym has microplates. If you would rather not do the bar arithmetic in your head, our plate loading calculator turns any of these numbers into the plates that go on each side.
The approximate rep column is derived by inverting the Epley formula, so it stays internally consistent with the estimate above it. Treat those numbers as orientation, not targets. Rep capacity at a given percentage varies enormously between people and between lifts — many lifters can grind out far more reps at seventy percent on a leg press than on a barbell squat.
When the estimate stops being reliable
This is the part most calculators skip, and it matters more than the arithmetic.
- Rep count is the biggest factor. These formulas were designed around low-rep sets. At two to five reps they are reasonable. By ten reps the error widens considerably, and past twelve the output is closer to a guess than an estimate. That is why the reps field caps at twelve.
- Proximity to failure changes everything. A set of five with three reps left in the tank and a set of five taken to genuine failure produce the same input but describe very different levels of effort. If you stopped well short, the estimate will read low.
- Rep endurance is individual. Two lifters with an identical five rep max can have genuinely different single rep maxes. Formulas assume an average relationship that no particular person is obliged to match.
- The lift matters. Estimates hold up better on compound barbell lifts than on isolation movements or machines, where the strength curve and stability demands differ.
- A max is not a fixed property. Sleep, stress, nutrition and where you are in a training block all move it. Yesterday’s estimate is not a permanent number.
The practical takeaway: use the estimate to set training loads, then adjust based on how the bar actually moves. If eighty percent feels like ninety, either your estimate is high or you are having a bad day, and both are useful information.
Tracking your estimated max over time
A single estimate is a snapshot. An estimate you can see trending across months is far more useful, because it tells you whether your programming is working. Logging apps calculate estimated maxes automatically from every set you record and chart them over time, which saves you doing this by hand after each session.
If you are choosing one, our Hevy app review and Strong app review cover how each handles estimated maxes, progression and set logging, and our head-to-head comparison covers the differences that actually matter day to day. If you want the wider field, we also compare the best strength training apps.
Training at home changes the maths, because loadable weight is often the limiting factor long before technique is. Our guide to adjustable dumbbells covers the practical weight ceilings of each system, which is worth knowing before you build a program around percentages you cannot actually load.
Frequently asked questions
Which formula is more accurate, Epley or Brzycki?
Neither is reliably better across all lifters and all lifts. The two agree exactly at ten reps; below that Epley reads higher, above it Brzycki does. At five reps or fewer the gap is usually small enough not to matter for programming. This calculator averages them and shows both so you can see the spread.
How many reps should I use for the most accurate estimate?
Three to five reps, taken close to failure with clean technique. That range is where these formulas behave best, and it is far less fatiguing and lower risk than a true max attempt.
Can I use this for dumbbell or machine exercises?
You can, but expect more error. The formulas were built around barbell lifts. On machines and isolation work the relationship between load and reps differs, so treat the output as a rough guide rather than a number to program precisely from.
Should I actually test my one rep max?
Only if you have a reason: a meet, a program that requires it, or curiosity backed by enough experience to attempt it safely. Testing is demanding and carries more risk than normal training. For most people training for strength or size, an estimate updated regularly is enough.
Why does the chart round the weights?
Because barbells load in plate increments. The chart shows the nearest loadable weight as the main figure, with the exact calculated value underneath in smaller text.