How to Calculate Your One Rep Max (5 Formulas Compared)
Quick Answer
To know how to calculate one rep max without actually attempting a maximal lift, use a submaximal set (ideally 2 to 10 reps, taken close to failure) and plug it into an estimation formula. The Epley formula and Brzycki formula are the two most common, but five established formulas exist, and they don't always agree with each other. All five, compared on the same numbers, plus a full 1RM percentage chart for programming your training weights, are below. For an instant result, use our one-rep max calculator.
Most guides stop at the Epley formula and call it done, but Epley is only one of several validated methods, and because each one was derived from a different research population and rep-range assumption, they can produce meaningfully different estimates from the identical set. Knowing more than one formula, and understanding where they diverge, gives you a far more honest picture of your actual strength than trusting a single number.
The Five Formulas
| Formula | Equation |
|---|---|
| Epley | 1RM = Weight × (1 + Reps ÷ 30) |
| Brzycki | 1RM = Weight × 36 ÷ (37 − Reps) |
| Lombardi | 1RM = Weight × Reps^0.10 |
| Mayhew et al. | 1RM = (100 × Weight) ÷ (52.2 + 41.9 × e^(−0.055 × Reps)) |
| O'Conner (Wathan) | 1RM = Weight × 100 ÷ (48.8 + 53.8 × e^(−0.075 × Reps)) |
The first two, Epley and Brzycki, are by far the most commonly cited in strength training research and programming software, which is why they are the ones our calculator applies. The other three are worth knowing because they were derived from different lifter populations, and comparing all five gives you a realistic range rather than a single potentially misleading number.
Worked Comparison: Same Set, Five Different Estimates
Input: 185 lbs lifted for 8 reps.
| Formula | Calculation | Estimated 1RM |
|---|---|---|
| Epley | 185 × (1 + 8÷30) | 234.3 lbs |
| Brzycki | 185 × 36 ÷ (37−8) | 229.7 lbs |
| Lombardi | 185 × 8^0.10 | 231.1 lbs |
| Mayhew | (100×185) ÷ (52.2 + 41.9×e^(−0.44)) | 228.9 lbs |
| O'Conner | 185×100 ÷ (48.8 + 53.8×e^(−0.60)) | 231.5 lbs |
Across five formulas, the estimates span from 228.9 to 234.3 lbs, a spread of about 5.4 lbs, or roughly 2.3% of the result. That is a normal, expected range, not an error in any single formula. Treating your true 1RM as falling somewhere in this range is more accurate than anchoring to one formula's exact number.
Why the Formulas Disagree More at Higher Rep Counts
The gap between formulas is not constant, as it widens as rep count increases. At 3 reps, most of these formulas land within a pound or two of each other. At 12+ reps, the spread can grow to 10 lbs or more on a moderately heavy lift.
This happens because every one of these formulas is an approximation built from a limited data set of real lifters, and the relationship between reps and strength is not perfectly linear, curving especially past about 10 reps in ways no single simple formula captures precisely. This is exactly why the 2 to 10 rep range is the generally recommended window for taking your test set.
Full 1RM Percentage Chart for Programming
Once you have an estimated max, most structured programs prescribe your actual working weight as a percentage of it, matched to a specific training goal:
| % of 1RM | Typical Rep Range | Primary Training Goal |
|---|---|---|
| 95 to 100% | 1 to 2 reps | Max strength / testing |
| 85 to 90% | 3 to 5 reps | Strength |
| 75 to 85% | 5 to 8 reps | Strength-hypertrophy |
| 65 to 75% | 8 to 12 reps | Hypertrophy (muscle growth) |
| 50 to 65% | 12 to 20 reps | Muscular endurance |
Example: Using the Epley estimate above (234 lbs), an 80% strength-hypertrophy working set would be 234 × 0.80 = 187.2 lbs, which you would typically round to the nearest 5 lbs on standard plates, resulting in 185 lbs.
Which Formula Should You Actually Use?
For practical training purposes, it rarely matters which of the five you pick, because the spread between them is small relative to the weight you are actually lifting, and all of them are only estimates of a number that shifts slightly day to day based on fatigue, sleep, and nutrition. The more useful habit is picking one formula and tracking it consistently over time.
If you are tracking recovery and strength together, our one-rep max calculator applies the Epley formula instantly, and since adequate protein intake directly supports strength gains, our protein calculator is worth pairing with your training numbers if muscle growth is part of your goal.
Frequently Asked Questions
No single formula is universally most accurate, as each was derived from a different lifter population. They tend to agree closely within the 2 to 10 rep range while diverging more at higher reps. Epley and Brzycki are the two most widely validated.
Because each formula approximates the relationship between submaximal reps and true max strength slightly differently based on its original sample data. A small spread between formulas is normal and expected.
Generally 2 to 10 reps, taken close to failure. Estimates become progressively less reliable above 10 to 12 reps because the mathematical relationship between reps and strength curves unpredictably at higher counts.
Multiply your estimated 1RM by the percentage matching your goal, roughly 85 to 90 percent for pure strength and 65 to 75 percent for hypertrophy, then round to a weight your available plates can load.
Testing a true 1RM carries higher injury risk, especially without a spotter or extensive lifting experience, and is generally recommended only for competitive lifters. For most training purposes, an estimated 1RM is safer and accurate enough.