You don’t need to actually attempt a single maximal lift to know roughly what it would be. This one rep max calculator estimates your 1RM, the most weight you could lift for exactly one rep, from a lighter set you’ve already done, using proven strength-science formulas. Enter the weight and reps from a recent set, and it returns your estimated 1RM along with a full training table showing what to lift at every percentage of that max.
How to use this one rep max calculator
- Choose your Units: Pounds (lb) or Kilograms (kg).
- Enter the Weight Lifted and the Repetitions Performed from a recent set, ideally between 1 and 10 reps for best accuracy.
- Select a 1RM Estimation Formula: Epley, Brzycki, or Lombardi in Simple mode, or switch to Advanced mode for McGlothin/Landers, Mayhew, O’Conner, Wathan, and an Average of All 7 option.
- Review your Estimated One Rep Max.
- Check “1RM by Formula” to compare how each formula estimates your max from the same set.
- Review the “Estimated Max Reps” table (how many reps you could likely do at various weights) and the “Training Load Percentages” table (what weight corresponds to each percentage of your 1RM, and the typical reps you’d manage there).
- Save your calculation or export it as an Image, PDF, or CSV.
What this one rep max calculator does
Every 1RM formula works from the same underlying idea: the heavier the weight and the fewer reps you can do with it, the closer that weight already is to your true one-rep max, and this relationship is well-documented enough that several independent formulas have been developed to estimate it mathematically. This calculator applies your chosen formula (or all of them at once, for comparison) to the weight and reps you entered, then builds out a full training table so the resulting number becomes something you can actually program around, not just a single estimated figure.
The seven 1RM formulas, explained
Each formula was derived from different data sets and rep ranges, which is why they don’t always agree exactly, and why comparing several gives a more complete picture than trusting just one.
Epley: 1RM = Weight × (1 + Reps ÷ 30)
Brzycki: 1RM = Weight × 36 ÷ (37 − Reps)
Lombardi: 1RM = Weight × Reps0.1
McGlothin/Landers: 1RM = (100 × Weight) ÷ (101.3 − 2.67123 × Reps)
Mayhew: 1RM = (100 × Weight) ÷ (52.2 + 41.9 × e−0.055 × Reps)
O’Conner: 1RM = Weight × (1 + 0.025 × Reps)
Wathan: 1RM = (100 × Weight) ÷ (48.8 + 53.8 × e−0.075 × Reps)
| Formula |
Best suited for |
| Epley |
One of the two most widely used formulas; a straightforward linear relationship, popular across general strength training |
| Brzycki |
The other most common formula; tends to run slightly more conservative than Epley at higher rep counts |
| Lombardi |
A simple power-function formula, one of the earliest published 1RM estimation methods |
| McGlothin/Landers |
A linear formula developed from powerlifting-specific data |
| Mayhew |
An exponential formula that tends to perform better at higher rep ranges (10-20 reps) |
| O’Conner |
A simple linear formula, one of the most conservative of the seven at higher reps |
| Wathan |
Another exponential formula, also better suited to higher rep ranges than the purely linear formulas |
Why the formulas sometimes disagree
Epley and Brzycki assume a straightforward linear decline in weight as reps increase, which holds up well in the 1-10 rep range most strength training actually happens in. Mayhew and Wathan instead use exponential curves, which are generally considered more accurate once you move into higher rep territory (10-20+ reps), since the relationship between weight and reps isn’t perfectly linear that far from a true 1RM. This is exactly why the calculator’s explainer recommends keeping your input set to 1-10 reps for the best accuracy regardless of which formula you choose, and why comparing multiple formulas, or using the Average of All 7 option, can give a more balanced estimate than relying on a single method.
Using the Estimated Max Reps table
This table works in the opposite direction from the main calculation: instead of estimating your 1RM from a set you did, it uses your estimated 1RM to predict roughly how many reps you could complete at various weights below your max. This is useful for programming, if you know your estimated 1RM, this table gives you a realistic rep expectation at any given percentage without needing to test it directly.
Using the Training Load Percentages table
Strength, hypertrophy, and endurance training all call for different percentages of your 1RM, and this table converts your estimated max directly into the actual weight to load for each common percentage, along with the typical rep range you’d expect to hit there.
| Training goal |
Typical %1RM range |
Typical rep range |
| Maximal strength |
85-100% |
1-5 reps |
| Strength/hypertrophy |
70-85% |
6-12 reps |
| Hypertrophy/endurance |
50-70% |
12-20+ reps |
Rather than guessing at what “70% of my max” actually weighs, this table hands you the specific number to load onto the bar for whatever percentage your program calls for.
Why 1-10 reps gives the most accurate estimate
Every one of these formulas was built from data within a specific rep range, and their accuracy degrades the further your input set strays from that range. A set of 3-5 reps close to failure tends to produce a more reliable 1RM estimate than a set of 20 reps, since a very high-rep set introduces more room for fatigue, pacing, and form breakdown to distort the relationship between weight and reps that these formulas assume.
A note on accuracy
Every formula here produces an estimate, not a guaranteed number. Actual 1RM varies by individual, technique, muscle fiber composition, and how fresh or fatigued you are on a given day, and no formula can fully account for all of that. If you do decide to test your actual one-rep max directly, always use a spotter and appropriate safety equipment, and warm up thoroughly beforehand, since a true maximal attempt carries meaningfully more injury risk than a submaximal set.
Frequently asked questions
Which 1RM formula is the most accurate?
There isn’t a single formula that’s most accurate for everyone. Epley and Brzycki are the two most widely used and tend to perform well in the 1-10 rep range. Mayhew and Wathan, which use exponential curves, tend to be more accurate at higher rep counts (10-20+). Using the “Average of All 7” option in Advanced mode gives a balanced estimate that isn’t overly dependent on any single formula’s assumptions.
Why does the calculator recommend using 1-10 reps for my input set?
All seven formulas were derived from data within roughly that rep range, and their accuracy declines the further an input set strays from it. A very high-rep set introduces more fatigue and pacing variability, which distorts the mathematical relationship these formulas rely on between weight and reps.
Should I actually test my 1RM directly instead of estimating it?
A direct test gives you your actual number rather than an estimate, but it also carries meaningfully more injury risk than a submaximal set, and requires a proper warm-up and a spotter. Many lifters use an estimated 1RM from a comfortable working set for day-to-day programming, and only test directly under safe, prepared conditions when it’s specifically useful to know the exact number.
How do I use the Training Load Percentages table in my program?
Once you have your estimated 1RM, the table converts common training percentages (for example 70%, 80%, 90%) directly into the actual weight to load, along with the typical rep range you’d expect to complete at that weight. This saves you from calculating each percentage by hand every time your program calls for a specific intensity.
