Complete Guide & Formula for the One-Rep Max Calculator
Your one-rep max (1RM) is the heaviest weight you can lift for a single, full-range rep of an exercise. Testing a true 1RM by maxing out on the bar is risky and fatiguing, so most lifters and coaches estimate it from a lighter set taken close to failure. This one-rep max calculator uses the two most widely trusted prediction formulas — Epley and Brzycki — to give you an instant, safe estimate you can build a training program around. Whether you're trying to calculate your one-rep max from a 5-rep set or need a quick max bench press estimator, this tool works for any major barbell lift.
💡 Epley vs. Brzycki Formula
Epley: 1RM = weight × (1 + reps ÷ 30). Brzycki: 1RM = weight × 36 ÷ (37 − reps). Epley tends to run slightly higher at higher rep counts, while Brzycki is considered more conservative past 10 reps. This calculator averages both so you get a balanced, realistic estimate.
Why Estimate Instead of Testing a True Max?
- Lower injury risk: No need to load a true single-rep max under fatigue.
- Faster programming: Instantly get training percentages (50–95% of 1RM) for strength, hypertrophy, or power blocks.
- Track progress: Re-test with a fresh working set every 4–6 weeks to see real strength gains.
- 100% Free & Private: All math runs in your browser — no signup, no data stored.
Accuracy & Key Variables
| Factor | Why It Matters | Tip |
|---|---|---|
| Weight lifted | The base load for both formulas | Use your most recent working set, not an old PR |
| Reps performed | Accuracy drops sharply above ~10 reps | For best accuracy, test in the 1–10 rep range |
| Set taken to failure? | Formulas assume the set was near-maximal effort | Use a set with 0–1 reps left in the tank |
Step-by-Step Instructions
- Enter the weight you lifted and how many clean reps you completed.
- Choose your unit (lb or kg), or tap a quick preset to test the tool.
- Click ⚡ Calculate One-Rep Max to see your estimated 1RM.
- Review the Epley and Brzycki breakdown plus the training-load table (50–95% of your 1RM) for programming your sets.
- Use the 📋 Copy Summary button to save your results, or 🔗 Share to send the calculator to a training partner.