A one-rep max, or 1RM, is the heaviest weight you can lift once with good form. Testing it directly is demanding, so many lifters estimate it from a lighter set taken to near failure. This calculator does that with two widely used equations, then builds a training ladder from 50% to 100% of the estimate.
Enter the weight you lifted and the reps you completed. Choose pounds or kilograms, and pick a single formula or the average of both.
How to Use the 1 Rep Max Calculator
- Enter the weight from your heaviest recent set.
- Set the reps with the stepper. Sets of about 2 to 10 reps work best.
- Choose a unit and formula. "Average" blends the Epley and Brzycki estimates.
The headline shows your estimated 1RM. The ladder below shows working weights at common percentages, which many programs use to set training loads.
The 1RM Formulas
| Formula | Equation |
|---|---|
| Epley | 1RM = weight × (1 + reps ÷ 30) |
| Brzycki | 1RM = weight × 36 ÷ (37 − reps) |
| Average | Mean of the Epley and Brzycki results |
The Brzycki equation was published by Matt Brzycki in the Journal of Physical Education, Recreation & Dance in 1993. The Epley equation comes from a 1985 strength training manual by Boyd Epley. Both give almost identical results at low reps and drift apart as reps increase.
A Worked Example
If you bench 185 lb for 5 reps, Epley gives 185 × (1 + 5 ÷ 30), or about 216 lb. Brzycki gives 185 × 36 ÷ 32, or about 208 lb. The average is about 212 lb, and 80% of that is roughly 170 lb.
How Accurate Are 1RM Estimates?
Prediction equations are useful, but they are estimates. A 1997 study in the Journal of Strength and Conditioning Research by LeSuer and colleagues tested seven equations in 67 untrained college students on the bench press, squat and deadlift. The predictions were closely correlated with tested maximums, but most equations showed significant errors for the bench press and squat, and all of them underestimated the deadlift.
A few practical points follow:
- Fewer reps usually means a closer estimate. Sets of high reps involve more endurance, which the equations do not capture well.
- Different lifts behave differently. An equation that suits one lift may underestimate or overestimate another.
- Training history matters. Experienced lifters and beginners respond differently to the same rep ranges.
This is why the calculator limits input to 15 reps and notes that accuracy drops above 10.
Using the Training Ladder
Many strength programs prescribe loads as a percentage of 1RM. The ladder shows those weights so you can plan sets without a separate calculation. Heavier percentages are used for lower-rep strength work, while lighter percentages suit higher-rep sets. The right loads for you depend on your program, goals and recovery.
Because the ladder is built from an estimate, treat the numbers as starting points. If a prescribed weight feels much too easy or too hard, adjust it.
Safety Before a True Max
A calculated 1RM lets many lifters train well without ever testing a true maximum. If you do attempt one, warm up thoroughly, use a spotter or safety equipment, and only test lifts you can perform with consistent technique. People with health conditions or injuries should get advice from a qualified professional before heavy lifting.
Strength training also pairs well with other forms of exercise. The comparison of Pilates vs strength training looks at how different approaches build strength. For cardio planning, the Heart Rate Zone Calculator estimates training zones from your age.
FAQs
How is a one-rep max calculated?
It is estimated from a lighter set. You lift a weight for as many good reps as you can, then an equation such as Epley or Brzycki converts that weight and rep count into a predicted single-rep maximum. The estimate is usually closest when the set is about 10 reps or fewer.
Which 1RM formula is most accurate?
No single formula is best for everyone or every lift. Research such as LeSuer and colleagues' 1997 study found that accuracy varied by exercise, with all tested equations underestimating the deadlift. Using the average of Epley and Brzycki smooths out some of the difference between them.
Why is there a 15-rep limit?
Equations become less reliable as reps increase, because high-rep sets depend heavily on muscular endurance. The calculator accepts up to 15 reps but notes that results above 10 reps are rougher. For the best estimate, use a set of roughly 2 to 10 reps.
Should I test my real one-rep max?
You do not need to. Many people train effectively with estimated maximums. If you do test, warm up well, use a spotter or safety bars, and only test lifts you perform with solid technique. Seek professional advice if you have an injury or health condition.
Does the calculator save my lifts?
No. The calculations run in your browser. Nothing you enter is stored, sent to analytics or shared, and refreshing the page clears your inputs.