Estimate your one-rep max (1RM) with the Brzycki formula from the weight and reps of one set, or find the working weight for 1 to 10 reps.
Safety note: This calculator provides an estimate only and may vary by individual. Don’t attempt a true 1RM based solely on this number—use appropriate warm-ups, safeties/spotters, and stop if you feel pain, dizziness, or unusual symptoms. If you’re new to lifting, returning from injury, pregnant, or have a medical condition, consider guidance from a qualified coach or clinician.
Brzycki Equation Formula
The Brzycki equation estimates your one-rep max from a weight you lifted for a low number of reps. Use low-repetition sets near fatigue. This calculator accepts 1 to 10 reps; ten is its upper boundary, not a guarantee of accuracy.
- 1RM = estimated one-rep max
- W = weight lifted for the performed reps
- R = number of reps performed
The calculator preserves two modes: estimate 1RM from lifted weight and repetitions, or estimate working weight from 1RM and target repetitions. Weight can be entered in pounds or kilograms; changing units converts the entered weight. The rearranged R expression is shown for reference, not as a third calculator mode. This tool uses the common 36/(37 − R) form, which differs slightly from formulas using rounded decimal coefficients.
Brzycki Rep Percentages
These percentages show the approximate share of your 1RM represented by each rep count under the Brzycki equation.
| Reps | Approx. % of 1RM | Example if 1RM is 200 lb |
|---|---|---|
| 1 | 100.0% | 200 lb |
| 3 | 94.4% | 189 lb |
| 5 | 88.9% | 178 lb |
| 8 | 80.6% | 161 lb |
| 10 | 75.0% | 150 lb |
Example Calculations
Example 1: Estimate 1RM from a 5-rep set
You lift 185 lb for 5 reps.
Your estimated 1RM is about 208 lb.
Example 2: Estimate weight for 8 reps
Your estimated 1RM is 120 kg, and you want to estimate an 8-rep weight.
The estimated 8-rep weight is about 96.67 kg.
FAQ
What is the Brzycki equation used for?
The Brzycki equation is used to estimate your one-rep max without testing a true max lift. You perform a set with a known weight and rep count, then use the formula to estimate the maximum weight you could lift for one rep.
How accurate is the Brzycki equation?
It is an estimate, not a guarantee. It is usually more useful for lower rep sets, especially 1 to 10 reps. Accuracy can vary based on the lift, your technique, fatigue, rest time, and how close the set was to failure.
Can I use the equation for more than 10 reps?
It is not recommended. Higher-rep sets tend to make 1RM estimates less reliable because muscular endurance becomes a larger factor. For best results, use a challenging set between 1 and 10 reps.
