Estimate your one-rep max from a weight and the reps you can lift.
Calculated instantly in your browser.
How do you calculate your one-rep max (1RM)?
Epley: 1RM = weight × (1 + reps ÷ 30). Brzycki: 1RM = weight × 36 ÷ (37 − reps). This tool averages both formulas. Estimates are most accurate at 1–10 reps. For example, lifting 100 kg for 5 reps gives an estimated 1RM of about 114.6 kg, and percentages help plan training loads.
Understanding your result
Estimates are most accurate at 1–10 reps. Use the percentages to plan training loads (e.g. 80% for sets of 8).
Formula and method
Epley: 1RM = weight × (1 + reps ÷ 30). Brzycki: 1RM = weight × 36 ÷ (37 − reps). This tool averages both.
Assumptions and limitations
This is an estimate, not medical or coaching advice, and results vary by individual, exercise and technique. The formulas are most reliable for lower rep counts and cannot account for your form, fatigue or lift type. Use the figure to guide training loads, progress gradually, and stop if anything causes pain or strain.
Worked example
Lifting 100 kg for 5 reps gives an estimated 1RM of about 114.6 kg.
How to use this tool
- Enter the weight you lifted.
- Enter how many reps you completed.
- Press Calculate.
About the One Rep Max Calculator
The One Rep Max Calculator estimates the most weight you could lift once, based on a set you can already do, and shows useful training percentages.
Who should use this tool
Lifters who want to estimate their one-rep max from a set they can already perform, without attempting a true maximal lift. Useful for planning training loads using percentage-based sets, and for tracking strength progress over time from everyday working sets.
Benefits
- Estimates one-rep max without a maximal attempt
- Averages the Epley and Brzycki formulas
- Provides training percentages for planning loads
- Recalculates instantly as you change the inputs
Practical use cases
- Estimating your max from a normal working set
- Setting percentage-based loads for training blocks
- Tracking your strength progress steadily over time
- Planning sets without testing a true one-rep max
Frequently asked questions
Should I actually try a 1-rep max?
Estimating from a sub-maximal set is safer. If you do test a true max, warm up thoroughly and use a spotter.
Why does the tool average two formulas?
The Epley and Brzycki formulas estimate one-rep max in slightly different ways and can disagree, especially as reps rise. Averaging them smooths out that difference and gives a more balanced figure than relying on either alone. It remains an estimate, most accurate when based on a set of roughly ten reps or fewer.
How do I use the training percentages?
The percentages express portions of your estimated one-rep max, so you can pick a load for a given rep range, such as around 80 percent for sets of eight. This helps structure training without maximal testing. Since the max is an estimate, adjust the weight to what feels appropriate on the day.