One Rep Max Calculator
Estimate your One Rep Max (1RM) without the risk of lifting your absolute limit. Our calculator uses several scientifically-backed formulas to give you the most accurate estimate possible.
What is One Rep Max?
One Rep Max (1RM) is the maximum amount of weight you can lift for a single repetition of a given exercise with proper form. It is considered the gold standard for measuring absolute strength in weightlifting and powerlifting.
Knowing your 1RM is essential for many strength programs, as they often prescribe training loads as a percentage of your maximum (e.g., "3 sets of 5 at 80% of 1RM").
Why Estimate Instead of Testing?
- Safety: Attempting a true 1RM puts significant stress on your joints and central nervous system, increasing the risk of injury.
- Frequency: You can estimate your 1RM frequently without needing a full recovery period.
- Convenience: You don't need a spotter or specialized equipment to estimate your max from a 5-rep or 10-rep set.
- Accuracy: For most lifters, these formulas are accurate within 2-5% of their actual max.
Limitations of 1RM Calculators
- High Rep Counts: Formulas become less accurate as the number of reps increases. They are most accurate for sets of 10 reps or fewer.
- Training Experience: Beginners may find the estimates less accurate as their technique often breaks down before their strength does.
- Exercise Type: Some formulas work better for upper body vs. lower body movements.
- Individual Variation: Some lifters are naturally better at high reps (slow-twitch dominant), while others are better at low reps (fast-twitch dominant).
The Formulas We Use
Brzycki: 1RM = w × (36 / (37 - r))
Lander: 1RM = (100 × w) / (101.3 - 2.67123 × r)
Lombardi: 1RM = w × r0.1
Mayhew et al.: 1RM = (100 × w) / (52.2 + (41.9 × e-0.055 × r))
O'Conner et al.: 1RM = w × (1 + 0.025 × r)
Wathen: 1RM = (100 × w) / (48.8 + (53.8 × e-0.075 × r))
Frequently Asked Questions
Most experts recommend testing a true 1RM no more than once every 3-4 months. However, you can use this calculator to estimate your progress every few weeks based on your training sets.
The Epley and Brzycki formulas are the most widely used and are generally very accurate for reps under 10. Our calculator provides an average of seven different formulas to give you a balanced estimate.
Yes, it works for any compound movement like the squat, bench press, deadlift, or overhead press. It is less useful for isolation exercises like bicep curls.
The calculator will still work, but the accuracy decreases as reps go up. For the best estimate, use a weight that you can lift for 3 to 8 reps.
No. Most of your training should be done between 65% and 85% of your 1RM. Training at 100% too often leads to burnout and injury.