How to use the one rep max calculator
- Enter the weight you successfully lifted for a given set.
- Select your preferred unit: pounds or kilograms.
- Type the number of repetitions you completed with that weight.
- Read the estimated one rep max values calculated by the Epley and Brzycki formulas.
How the Formulas Work
A one rep max calculator estimates the heaviest load you could lift for a single repetition based on a lighter set taken close to failure. The two most widely used equations are the Epley formula and the Brzycki formula.
The Epley formula multiplies the lifted weight by a factor derived from the repetition count:
1RM = weight x (1 + reps / 30)
For example, lifting 225 lb for 5 reps gives 225 x (1 + 5/30) = 225 x 1.1667 = 262.5 lb.
The Brzycki formula divides the weight by a decreasing fraction:
1RM = weight x 36 / (37 - reps)
Using the same numbers: 225 x 36 / (37 - 5) = 225 x 36 / 32 = 253.125 lb. Both formulas converge when reps equals 1, returning the exact weight lifted.
Common One Rep Max Estimates
The table below shows how different repetition ranges translate into a percentage of your estimated one rep max using the Epley formula. These percentages help coaches prescribe training loads without testing a true maximum.
| Reps | % of 1RM (Epley) | Example: 1RM = 300 lb |
|---|---|---|
| 1 | 100% | 300 lb |
| 3 | 90.9% | 273 lb |
| 5 | 85.7% | 257 lb |
| 8 | 78.9% | 237 lb |
| 10 | 75.0% | 225 lb |
| 12 | 71.4% | 214 lb |
Keep in mind these are estimates. Individual variation means some lifters perform better at higher repetitions while others excel at singles.
Accuracy and Repetition Ranges
The accuracy of any 1rm calculator depends heavily on the number of repetitions used as input. Sets of 1 to 5 reps produce the most reliable estimates because fatigue mechanics at low repetitions closely mirror those of a maximal single effort.
When you use sets of 8 to 10 reps, the estimate remains useful but carries more variance. Beyond 10 to 12 repetitions, muscular endurance becomes the limiting factor rather than absolute strength, and the formulas tend to overestimate your true one repetition maximum. For the best results, choose a weight you can lift for 3 to 5 clean reps with good form.
Practical Uses in Training
Strength athletes use one rep max estimates to structure periodized programs. Powerlifting templates often prescribe work sets as percentages of a known or estimated max. For instance, a volume block might call for 5 sets of 5 at 75% of your 1RM.
Rather than testing a true maximum every few weeks, which taxes recovery and raises injury risk, lifters plug recent working sets into this one rep max calculator to track progress. If your 5 rep max on squats increases from 275 lb to 285 lb, the calculator shows your estimated max has risen accordingly, confirming the program is working.
This approach pairs well with cardiovascular assessments like a vo2 max calculator for athletes who train both strength and endurance.
Epley vs Brzycki: Which to Trust
The Epley formula tends to give slightly higher estimates at moderate repetition ranges (5 to 10), while the Brzycki formula is more conservative. Research comparing the two shows neither is universally superior; they simply model the strength-endurance curve differently.
A practical approach is to look at both outputs. If your training program calls for 85% of your max, calculate that percentage from both the Epley and Brzycki values and pick the load that matches your perceived exertion. Over time, you will learn which formula aligns better with your actual performance on heavy singles.
An estimate, not medical advice
The one rep max calculator uses a standard published formula, and formulas describe averages, not you. Age, body composition, medical conditions, medication, pregnancy and training history can all move the real number. Use the result as a starting point for planning, and speak to a doctor, dietitian or qualified coach before making health, diet or training decisions, especially if you have a medical condition.
Worked examples
Each result below was produced by the same code the tool runs, so you can check your own numbers against them.
| Example | Input | Result |
|---|---|---|
| 225 lb for 5 reps | Weight lifted: 225; Unit: lb; Repetitions performed: 5 | Epley 1RM: 262.5 lb; Brzycki 1RM: 253.13 lb; Average estimate: 257.81 lb; 75% for volume work: 193.36 lb; 85% for strength work: 219.14 lb |
| 100 kg for 3 reps | Weight lifted: 100; Unit: kg; Repetitions performed: 3 | Epley 1RM: 110 kg; Brzycki 1RM: 105.88 kg; Average estimate: 107.94 kg; 75% for volume work: 80.96 kg; 85% for strength work: 91.75 kg |
| 185 lb for 8 reps | Weight lifted: 185; Unit: lb; Repetitions performed: 8 | Epley 1RM: 234.33 lb; Brzycki 1RM: 229.66 lb; Average estimate: 231.99 lb; 75% for volume work: 174 lb; 85% for strength work: 197.2 lb |
| Single rep (known max) | Weight lifted: 315; Unit: lb; Repetitions performed: 1 | Epley 1RM: 315 lb; Brzycki 1RM: 315 lb; 75% for volume work: 236.25 lb; 85% for strength work: 267.75 lb |
FAQ
What is a one rep max?
A one rep max (1RM) is the heaviest weight you can lift for a single repetition of a given exercise with proper form. It is the standard measure of absolute strength in powerlifting and strength training.
Is it safe to test my true one rep max?
Testing a true 1RM carries injury risk, especially for beginners. Using a one rep max calculator with a submaximal set of 3 to 5 reps provides a reliable estimate without the strain of an all-out single.
Which formula is more accurate, Epley or Brzycki?
Both are well validated. Epley tends to estimate slightly higher at 5 to 10 reps, while Brzycki is more conservative. For sets under 5 reps, the difference between them is minimal.
Can I use this calculator for any exercise?
Yes. The formulas apply to barbell squats, bench presses, deadlifts, overhead presses, and other compound movements. They are less reliable for isolation exercises where technique breakdown happens differently.
Why does the estimate seem too high when I use 15 reps?
At high repetition counts, local muscular endurance limits the set before maximal strength is truly tested. The mathematical models extrapolate linearly, which overestimates your 1RM beyond about 10 reps.
Does the unit (pounds vs kilograms) change the result?
No. The formulas are ratio-based, so the output scales proportionally with whatever unit you enter. Just ensure you read the result in the same unit you provided.