1RM Calculator
Estimate your one-rep max from a submaximal set using proven strength formulas.
Tip: predictions are usually most reliable when your reps are between 2 and 10.
What is a 1RM and why lifters track it
Your 1RM (one-rep max) is the maximum load you can lift for a single repetition with good form. In strength training, your 1RM acts like a benchmark: it helps you set working weights, monitor progress, and structure training blocks for goals like powerlifting, athletic performance, or muscle gain.
Testing a true one-rep max can be useful, but it can also be fatiguing and risky if done too often. That's why many coaches rely on a 1RM calculator formula based on a safer multi-rep set, like 5 reps at a challenging weight.
Popular 1RM calculator formulas
Different formulas estimate 1RM in slightly different ways. None is perfect for every person, but most are close enough for practical programming.
Epley: 1RM = weight × (1 + reps / 30)
Brzycki: 1RM = weight × 36 / (37 − reps)
Lombardi: 1RM = weight × reps0.10
O'Conner: 1RM = weight × (1 + 0.025 × reps)
Mayhew: 1RM = 100 × weight / (52.2 + 41.9 × e−0.055 × reps)
Wathan: 1RM = 100 × weight / (48.8 + 53.8 × e−0.075 × reps)
Which formula should you use?
- Epley and Brzycki are the most common in gyms and coaching apps.
- Mayhew and Wathan can fit higher-rep sets a little better for some lifters.
- Using an average of several formulas often gives a balanced estimate and reduces formula bias.
How to use this calculator correctly
Step-by-step
- Pick a lift (bench press, squat, deadlift, overhead press, etc.).
- Perform a hard set with clean form, stopping before technique breaks down.
- Enter the exact weight and reps completed.
- Select your preferred formula (or the average option).
- Use the result to set your training percentages for upcoming sessions.
Simple example
If you bench press 185 lb for 5 reps, a typical predicted 1RM is around 210–220 lb depending on the formula used. That range is normal, and it's why many lifters use trends over time instead of obsessing over a single number.
Using your estimated 1RM in a program
Once you have an estimate, your training plan becomes easier to scale. Most programs prescribe intensity as a percentage of 1RM:
- 60–70%: technique work, speed work, warm-up volume
- 70–80%: hypertrophy and moderate strength volume
- 80–90%: heavy strength work
- 90%+: low-rep peak work for advanced lifters
The calculator above automatically generates a percentage table so you can quickly see useful loads for your next workout.
Accuracy, limits, and safety notes
A 1RM formula is an estimate, not an absolute truth. Real-world values change with sleep, stress, nutrition, exercise technique, and lift-specific skill. Your bench press prediction may be very accurate while your deadlift estimate is slightly off, or vice versa.
- Best accuracy usually comes from sets in the 2–10 rep range.
- Very high-rep sets can overestimate or underestimate your true max.
- Always prioritize safe technique over squeezing out extra reps for the calculator.
- If you have pain or medical concerns, consult a qualified coach or healthcare professional before max testing.
FAQ: 1rm calculator formula
Can beginners use a 1RM calculator?
Yes. In fact, beginners often benefit from estimated maxes rather than true max attempts. It's safer and still useful for planning progress.
Should I update my 1RM every week?
You can update estimates every 2–6 weeks, or whenever your top sets clearly improve. Frequent updates help maintain appropriate training loads.
Why does each formula give a different result?
Each equation was built from different datasets and assumptions. Small differences are expected. Look at long-term trends and performance in training, not just one number.
Is estimated 1RM good enough for powerlifting prep?
For most training weeks, yes. Closer to competition, lifters usually test heavier singles to dial in attempt selection more precisely.