How a one-rep max is estimated
Your one-rep max (1RM) is the heaviest weight you can lift once with good form. Testing it directly means working up to an all-out single, which is tiring and riskier. Instead, you can lift a lighter weight for as many reps as you can and estimate the 1RM from the result. The fewer reps you can do, the closer the weight is to your max.
The calculator runs seven published equations, where w is the weight lifted and r the reps completed:
Brzycki: 1RM = w × 36 ÷ (37 − r)
Lombardi: 1RM = w × r^0.10
O’Conner: 1RM = w × (1 + 0.025 × r)
Mayhew: 1RM = 100 × w ÷ (52.2 + 41.9 × e^(−0.055 × r))
Wathan: 1RM = 100 × w ÷ (48.8 + 53.8 × e^(−0.075 × r))
Lander: 1RM = 100 × w ÷ (101.3 − 2.67123 × r)
Each formula was fitted to a different group of lifters and exercises, so they disagree a little. The default result is their average, which evens out the quirks of any single equation. If your coach or program uses one formula, pick it from the list. A set of one rep is your max, so every formula returns the weight itself.
Worked examples
Example 1: bench press, 225 lb for 5 reps.
- Epley: 225 × (1 + 5 ÷ 30) = 225 × 1.1667 = 262.5 lb
- Brzycki: 225 × 36 ÷ 32 = 253.1 lb
- Average of all seven: 259.9 lb, about 260 lb, or 117.9 kg.
The formulas range from 253 to 268 lb here, a spread of about 6%. That is typical for a five-rep set.
Example 2: squat, 100 kg for 5 reps. Epley gives 116.7 kg, Brzycki 112.5 kg, Mayhew 119.0 kg, and the average is 115.5 kg. Rounded to the nearest 2.5 kg plate step, that is 115 kg.
Example 3: a lighter set, 60 kg for 10 reps. Epley and Brzycki both give exactly 80 kg at ten reps; the average of all seven is 78.6 kg. The estimate is still useful, but higher-rep sets depend more on muscular endurance, so the calculator warns above 10 reps.
Training percentages
Once you know your 1RM, programs prescribe weights as a percentage of it. The table under the calculator lists 50% to 100% with the reps you can expect, worked out by solving the Epley equation for reps. Real numbers vary between people and exercises, so treat them as a guide.
| % of 1RM | Reps you can expect | Typical use |
|---|---|---|
| 100% | 1 | Testing a max |
| 95% | 2 | Heavy singles and doubles |
| 90% | 3 | Strength |
| 85% | 5 | Strength |
| 80% | 8 | Strength and muscle growth |
| 75% | 10 | Muscle growth |
| 70% | 13 | Muscle growth and endurance |
| 65% | 16 | Muscular endurance |
| 60% and below | 20+ | Warm-ups, technique, endurance |
The National Strength and Conditioning Association’s load guidelines group these loosely: about 85% or more for strength (6 reps or fewer), 67–85% for muscle growth (6–12 reps) and under 67% for muscular endurance (12 or more reps).
Tips for an accurate estimate
- Use a set of 3 to 6 reps. Studies such as LeSuer and colleagues (1997) found most equations predict well from sets of 10 reps or fewer, and the closer to failure you go, the better.
- Count only clean reps. A rep with a big change in form, a bounce or a partial lockout should not count.
- Test when fresh. Do the set early in a session after a proper warm-up, not after other heavy work.
- Compare like with like. Estimates are exercise-specific. Your bench press 1RM tells you nothing about your squat.
- Re-estimate every few weeks. As you get stronger, update the number so your training percentages keep up.
Safety
If you do test a true one-rep max, warm up with several lighter sets, use a spotter or safety bars, and stop if your technique breaks down. Beginners usually do not need to test a 1RM at all; working from estimated maxes is enough for the first year or two of training. Anyone with heart disease, high blood pressure or a recent injury should check with a doctor before maximal lifting.
Fuel your training
Strength gains depend on eating enough. Set a daily protein target with the protein calculator, find your calories with the calorie calculator and split them with the macro calculator. To convert plate weights between kilograms and pounds, use the weight converter.