Strength tool
One-Rep Max Calculator
Estimate the heaviest single repetition you could perform from a submaximal working set.
Understanding your one-rep max
Your one-rep max (1RM) is the heaviest weight you could lift for a single, full repetition of an exercise. Instead of risking a true maximal attempt, this tool estimates it from a normal working set using a proven strength formula.
How to use it
- 1Pick a set you performed with solid technique, ideally 10 reps or fewer.
- 2Enter the weight you lifted in kilograms.
- 3Enter the number of clean repetitions you completed.
- 4Select Calculate to see your estimated one-rep max.
How it helps your fitness
Knowing your 1RM lets you pick the right weight for a goal—heavier percentages for strength, moderate ones for muscle—without guessing. Re-estimating it over time is a clear, motivating way to prove your strength is going up.
What the numbers mean
- 1RM
- The estimated maximum weight you could lift once with good form.
- Reps
- How many repetitions you completed; fewer reps give a more accurate estimate.
- % of 1RM
- Training loads are often set as a percentage—e.g. strength work near 85–95%, muscle building near 67–85%.
- Kilograms (kg)
- The result is shown in kilograms, ready to load on the bar.
Keep in mind
This is an estimate, and it becomes less accurate above about ten reps. Always warm up thoroughly, keep good form, and treat the number as a training guide rather than a target to max out on without preparation.