One Rep Max Calculator
Estimate your one rep max (1RM) from any weight and rep count. This one rep max calculator uses the Epley and Brzycki formulas and builds a training percentage chart for every rep range.
Reviewed & updated for 2026 by Rakesh Choudhary, PhD · How we calculate
Your training percentage chart
Working weights based on your estimated 1RM, the percentage you use depends on whether you're training for strength, size, or endurance:
| % of 1RM | Est. reps | Goal | Weight |
|---|---|---|---|
| Enter a lift to build your chart | |||
How 1RM is estimated
Your one rep max is the most weight you can lift for a single rep with good form. Testing it directly is risky, so coaches estimate it from a set you can already do. The two most common formulas are Epley (1RM = weight × (1 + reps ÷ 30)) and Brzycki (1RM = weight × 36 ÷ (37 − reps)). This calculator shows both and averages them.
Estimates are most accurate in the 1–5 rep range. Above roughly 10 reps, fatigue and technique vary so much that the number becomes a rough guide. For tracking progress, keep the rep count and exercise consistent and watch the estimate trend up over weeks.
For general fitness reference. Warm up, use a spotter, and progress gradually, don't load your estimated max without preparation.
Worked example: estimating from a real set
Suppose you bench press 185 lb for 5 clean reps. The two most-used formulas estimate your one-rep max like this:
- Epley: weight × (1 + reps ÷ 30) = 185 × (1 + 5 ÷ 30) = 185 × 1.167 = 216 lb.
- Brzycki: weight × 36 ÷ (37 − reps) = 185 × 36 ÷ 32 = 185 × 1.125 = 208 lb.
The two agree within a few percent at low reps and drift apart as reps climb, which is why every 1RM estimate is most reliable from sets of about 2 to 6 reps. Above 10 reps, fatigue and form make the number a rough guide at best. The calculator above averages across established formulas and applies your result to the percentage chart so you can program your working sets.
FAQs
How do you calculate one rep max?
Enter a weight you lifted and the number of clean reps, then a formula estimates the max you could lift once. The popular Epley formula is 1RM = weight × (1 + reps ÷ 30). For example, 185 lb for 5 reps ≈ 185 × (1 + 5/30) = 216 lb. The calculator averages several formulas for a more reliable estimate.
What is the Epley vs Brzycki formula?
Both estimate 1RM from submaximal lifts. Epley: 1RM = w × (1 + reps/30). Brzycki: 1RM = w × 36 ÷ (37 − reps). They agree closely at low reps and diverge above about 10 reps, where all 1RM estimates become less accurate. This tool shows both and an average.
How accurate is a 1RM estimate?
Most accurate at 1–5 reps, where estimates are usually within a few percent of a true max. Accuracy drops as reps rise, because endurance and technique vary more, so a 1RM estimated from a 15-rep set is a rough guide, not a number to load on the bar blindly. Test true maxes carefully with a spotter.
What percentage of 1RM should I train at?
It depends on the goal. Strength: 85–100% for 1–5 reps. Hypertrophy (muscle size): 67–85% for 6–12 reps. Endurance: under 67% for 12+ reps. The percentage chart on this page converts your estimated 1RM into working weights for each rep range.
Should I actually attempt my estimated 1RM?
Not without preparation. Use the estimate to program training weights, then test a true 1RM only when well rested, warmed up, and with a spotter or safety bars. Beginners generally shouldn't max out, rep-based estimates are safer and nearly as useful for tracking progress.