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Estimate your 1RM without pretending it is exact.
Enter a completed weight and repetition count. Compare two established formulas, see the estimate range, and build a practical percentage chart.
Works with pounds or kilograms. No signup. Your inputs stay in this browser.
Calculate estimated 1RM
Use a technically consistent set completed close to failure.
Everything runs locally. Nothing is saved or transmitted.
Your 1RM percentage chart
These loads are calculated from the midpoint of the Epley and Brzycki estimates. Round them to equipment you can load safely and treat the table as planning context.
| Percentage | Estimated load | Use |
|---|
How the calculator works
Forma shows both equations because different formulas can produce different answers from the same set. The gap is useful evidence of uncertainty.
Epley equation
The Epley estimate increases the completed load according to the number of repetitions performed.
Brzycki equation
The Brzycki estimate divides the completed load by a repetition-based percentage.
What improves usefulness
- Use the same exercise, setup, range of motion, and technique.
- Prefer a lower-repetition set completed close to failure.
- Compare estimates over time rather than treating one number as proof.
- Keep the unit and equipment consistent.
What creates error
- High-repetition sets and uncertain proximity to failure.
- Technique, range of motion, tempo, or equipment changes.
- Exercise-specific strength-endurance differences.
- Fatigue, pain, motivation, and unfamiliar testing conditions.
Research and limitations
Submaximal prediction avoids a direct maximal attempt, but it does not remove uncertainty. Published equations differ, and their validity depends on the exercise, population, load, and repetition count used to develop or test them.
LeSuer and colleagues compared multiple equations against measured 1RM performance and found that accuracy differed by formula and exercise.
A validation study in collegiate football players reported that equation validity depended on the number of repetitions, with higher validity when fewer repetitions were completed.
A recent cross-validation compared 18 published equations for bench press and leg extension, illustrating why one generic equation should not be treated as universally exact.
This tool publishes the two formulas it uses and reports their range. It does not use or reveal Forma’s proprietary progression model. It is educational, not medical advice, and it does not determine whether maximal lifting is appropriate for you.
1RM calculator FAQ
What is a one rep max?
A one repetition maximum is the greatest load you can complete for one repetition of a specific exercise under defined technique and testing conditions.
How accurate is an estimated 1RM?
It varies. The equation, exercise, lifter, technique, proximity to failure, and repetition count all matter. Use the estimate for programming and longitudinal comparison, not as a guaranteed maximal lift.
Which formula is best?
No single generic equation is best for every exercise and lifter. This calculator shows Epley and Brzycki separately, then uses their midpoint as a convenient planning estimate.
How many repetitions should I use?
Lower-repetition sets generally produce more useful estimates than high-repetition sets. This tool accepts up to 20 repetitions but shows an extra caution when the input exceeds 10.
Should I test my true 1RM?
You do not need a true 1RM to track progress. If you choose to test, use appropriate preparation, technique, safety equipment, and competent supervision for your experience and the exercise.
Follow the trend, not one calculated number.
Forma keeps estimated strength beside load, repetitions, optional RIR, exercise history, weekly muscle volume, nutrition, bodyweight, and steps.