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Browse all calculatorsEnter the weight and the reps you completed. Seven published formulas estimate your one rep max in kg or lb, with the spread between them shown.
This is a general estimate for educational use. It is not medical advice, a diagnosis or a treatment plan, and it is not coaching advice. Talk to a doctor, qualified coach or other qualified professional before you change your exercise or attempt a heavy lift.
| Formula | Equation | 1RM | vs average |
|---|
| Reps | Weight | % of 1RM |
|---|
| % of 1RM | Weight | Reps |
|---|
Private by design. Everything runs in your browser and is never uploaded.
A one rep max (1RM) is the heaviest weight you can lift once with good form. A 1RM calculator estimates it from a lighter set: enter the weight and the reps completed. For example, 100 kg for 5 reps is about 116.7 kg by the Epley formula, weight × (1 + reps ÷ 30).
This one rep max calculator runs seven published formulas at once, shows the average and how far apart they are, and builds a table of the weight for any number of reps. Results change as you type, in kg or lb, and the working is written out under the result. To turn any weight into a percent, the percentage calculator does the arithmetic, and the free online calculators page lists the rest.
| Set | Epley | Brzycki | Average of 7 | Lowest to highest |
|---|---|---|---|---|
| 100 kg × 1 rep | 100.0 | 100.0 | 100.0 | 100.0 to 100.0 |
| 100 kg × 5 reps | 116.7 | 112.5 | 115.5 | 112.5 to 119.0 |
| 225 lb × 3 reps | 247.5 | 238.2 | 245.9 | 238.2 to 256.5 |
| 80 kg × 8 reps | 101.3 | 99.3 | 99.8 | 96.0 to 102.1 |
| 60 kg × 12 reps | 84.0 | 86.4 | 82.6 | 76.9 to 86.6 |
| 40 kg × 20 reps | 66.7 | 84.7 | 67.9 | 54.0 to 84.7 |
The first answer is already on screen. Change any number and it updates at once, with no Calculate button.
Type the weight, pick kg or lb, and set the reps you completed from 1 to 30. A comma works as a decimal point, so 102,5 is read as 102.5.
The headline is the average of seven formulas. The range and the spread show how much they disagree, and the formula chips switch the headline to a single formula.
Set the target reps to see the weight for that many reps. The tables list every rep count and every 5% step, and can round to the nearest 1, 2.5 or 5.
Copy the result as one line of text, or share a link that opens the calculator with the same weight, reps and options.
Every formula takes the weight lifted (w) and the reps completed (r) and multiplies w by a number that grows with r. Because the unit cancels out, the same formula works in kg and lb. The equations come from different authors and data, which is why the seven answers differ.
Turning the equation around gives the weight for any rep count: divide the 1RM by the same multiplier. With the Epley formula, 8 reps is 1RM ÷ (1 + 8 ÷ 30), about 79% of the max. One rep is treated as the max itself, because Epley is stated for more than one rep and several formulas would otherwise add a few percent to a single rep.
| Formula | Estimated 1RM | Weight for r reps, % of 1RM |
|---|---|---|
| Epley | w × (1 + r ÷ 30) | 100 ÷ (1 + r ÷ 30) |
| Brzycki | w × 36 ÷ (37 − r) | 100 × (37 − r) ÷ 36 |
| Lombardi | w × r0.10 | 100 ÷ r0.10 |
| Mayhew | 100 w ÷ (52.2 + 41.9 e−0.055 r) | 52.2 + 41.9 e−0.055 r |
| O’Conner | w × (1 + 0.025 r) | 100 ÷ (1 + 0.025 r) |
| Wathan | 100 w ÷ (48.8 + 53.8 e−0.075 r) | 48.8 + 53.8 e−0.075 r |
| Lander | 100 w ÷ (101.3 − 2.67123 r) | 101.3 − 2.67123 r |
Each cell is the share of the one rep max that a set of that many reps stands for, rounded to a whole percent. The columns sit closest together at around 5 to 6 reps and drift apart as the reps rise; a published chart of these formulas notes that they diverge greatly after about 10 reps.
| Reps | Epley | Brzycki | Lombardi | Mayhew | O’Conner | Wathan | Lander | Average |
|---|---|---|---|---|---|---|---|---|
| 1 | 100% | 100% | 100% | 100% | 100% | 100% | 100% | 100% |
| 2 | 94% | 97% | 93% | 90% | 95% | 95% | 96% | 94% |
| 3 | 91% | 94% | 90% | 88% | 93% | 92% | 93% | 91% |
| 4 | 88% | 92% | 87% | 86% | 91% | 89% | 91% | 89% |
| 5 | 86% | 89% | 85% | 84% | 89% | 86% | 88% | 87% |
| 6 | 83% | 86% | 84% | 82% | 87% | 83% | 85% | 84% |
| 7 | 81% | 83% | 82% | 81% | 85% | 81% | 83% | 82% |
| 8 | 79% | 81% | 81% | 79% | 83% | 78% | 80% | 80% |
| 9 | 77% | 78% | 80% | 78% | 82% | 76% | 77% | 78% |
| 10 | 75% | 75% | 79% | 76% | 80% | 74% | 75% | 76% |
| 12 | 71% | 69% | 78% | 74% | 77% | 71% | 69% | 73% |
| 15 | 67% | 61% | 76% | 71% | 73% | 66% | 61% | 67% |
| 20 | 60% | 47% | 74% | 66% | 67% | 61% | 48% | 59% |
| 25 | 55% | 33% | 72% | 63% | 62% | 57% | 35% | 50% |
| 30 | 50% | 19% | 71% | 60% | 57% | 54% | 21% | 38% |
Many one rep max calculators use one formula, accept 1 to 10 reps and give a single number. These are the details that change what you read.
| Feature | Basic 1RM calculator | This calculator |
|---|---|---|
| Formulas | One, often not named | Seven named formulas, each shown with its equation |
| Agreement | A single number with no sense of error | Average, lowest to highest, and the spread in percent |
| Reps | Often 1 to 10 | 1 to 30, with a warning above 10 reps |
| Results | May need a Calculate button or a page reload | Updates as you type, with an answer on first load |
| Weight for a rep target | A fixed table | Any target from 1 to 30 reps, rounded to 1, 2.5 or 5 if you like |
| Units | kg or lb, no conversion shown | kg or lb, with the other unit beside the result |
| Working | Answer only | Every step written out, with the rounding rule |
| Safety wording | Rarely mentioned | Reps, spotter and not-coaching notes beside the result |
Many programs write loads as a percent of the one rep max. Enter a recent set to see what 70%, 80% or 90% works out to in kg or lb.
Put a set of 5 and a set of 8 on the same lift through the calculator to see whether the estimates agree, and how big the spread is.
Many lifters never test a true max. A lighter set gives an estimate without the risk of a maximal attempt.
Set the target reps, for example 8, and read the weight that rep count stands for, rounded to the plates you have.
Copy the one-line result into the online notepad to keep a log of your sets that stays on your device.
Gyms load bars in kg or lb. Pick the unit you lift in and the other one is shown beside the result.
This page gives estimates and does not tell anyone what to lift. These points explain how far to trust the numbers.
Research found the equations more accurate when a set ended at fewer than about 10 reps. The warning on the result appears above that.
A true one rep max is a maximal load, so a spotter or safety bars are the usual precaution. An estimate from a lighter set avoids the attempt.
The formulas cannot see technique, rest, fatigue or the exercise, so two lifters with the same set can have different real maxes.
A single rep at a weight returns that weight from every formula, so the spread is zero.
Round the table weights to 1, 2.5 or 5 to see loads that match the plates you have. The 1RM itself stays unrounded.
Strength estimates sit apart from body numbers. For energy use see the calories burned calculator, and for body composition the lean body mass calculator.
The result is a prediction from published equations. A tested max can differ, and the spread shows part of that doubt. See the Wikipedia article on the one-repetition maximum for background.
It does not plan training, judge technique or check your health. It is meant for people aged 14 and over. Talk to a doctor or a qualified coach before attempting a heavy lift.
Reps run from 1 to 30 and the weight is capped at 2,000 kg or lb. Brzycki is only defined below 37 reps, and the cap keeps every formula in range.
The equations and their constants are the ones listed in the Wikipedia article below. The original papers were not opened for this page, so check the constants against them before using the numbers in research. The accuracy and safety notes come from the two papers listed.
Short answers about estimating a 1RM, the formulas and their limits.
A one rep max is the heaviest weight a person can lift for a single repetition of an exercise with the technique they normally use. It is usually discussed for lifts such as the bench press, squat and deadlift, and training programs often write loads as a percent of it.
Take a set you have already completed and note the weight and the number of reps. With the Epley formula the estimate is the weight × (1 + reps ÷ 30), so 100 kg for 5 reps gives 100 × (1 + 5 ÷ 30) = 116.7 kg. This calculator runs seven formulas at once and shows the average and the spread.
No single formula is best for every lift or every person. Studies compare equations with a tested max, and the results depend on the exercise, the people tested and the number of reps. One study of women found the equations more accurate when sets ended at fewer than 10 reps, which is why this calculator shows all seven and the spread between them.
The formulas come from different authors and data, so each treats the number of reps differently. The highest and lowest of the seven differ by about 7 percent of their average at 3 reps, 6 percent at 5 reps, 7 percent at 10 reps and 45 percent at 20 reps. The spread figure shows how far apart they are for your own set.
Research found prediction equations more accurate when a set ended at fewer than about 10 reps, and the formulas drift further apart above that. The calculator accepts 1 to 30 reps so you can compare, and it adds a warning to any result above 10 reps.
A true one rep max is a maximal load, and a research paper notes that the safety of maximal testing has been questioned, especially for people new to it. A spotter or safety bars (safeties) are the usual precaution. This page only estimates a max from a lighter set, it never tells anyone to attempt one, and it is not coaching advice.
A single rep at a weight is already a one rep max for that day, so the calculator returns the weight lifted for every formula. Epley is stated for more than one rep, and the other formulas would add up to about 9 percent to a single rep, so one rep is treated as the max itself.
Set the target reps box under the formula chips. The calculator multiplies the estimated 1RM by the percent that many reps stands for, for example about 80 percent for 8 reps by the average of the seven formulas, and it can round the answer to the nearest 1, 2.5 or 5.
It lists the weight at each percent of the estimated max and the most whole reps that percent allows by the chosen formula. With the Epley formula, 75 percent of a max is about 10 reps and 60 percent is about 20 reps.
No. Each formula multiplies the weight lifted by a number that depends only on the reps, so the answer scales with the unit. The calculator shows the result in your unit and in the other one, using 1 lb = 0.45359237 kg.
The formulas use only weight and reps, so they cannot see the exercise, your technique or your fatigue. Studies found that which equations predicted a lift well differed between the bench press and the squat, so treat the result as an estimate and not a measurement.
No. Everything is calculated in your browser and nothing is sent to a server. The numbers appear in the page address only so a shared link opens with the same set, and your kg or lb choice is remembered on your own device.