How the one-rep max calculator works
Your one-rep max, or 1RM, is the heaviest weight you can lift for a single repetition of an exercise. Testing it directly is tiring and, with heavy compound lifts, risky — so most lifters estimate it instead from a set done with a lighter weight and more reps.
This tool uses two well-known estimation formulas and averages them. The Epley formula is 1RM = weight × (1 + reps ÷ 30). The Brzycki formula is 1RM = weight × 36 ÷ (37 − reps). Both return the weight itself for a single rep and predict a higher max as the rep count rises; averaging them smooths out their individual quirks.
Once you have an estimated 1RM, the percentage table turns it into practical working weights. As a rough guide, sets of 1 sit near 100%, sets of 2 near 95%, sets of 4 near 90%, sets of 6 near 85%, sets of 8 near 80%, sets of 10 near 75% and sets of 12 near 70%.
Reference note: estimates are most reliable for sets of about 1–6 reps and lose accuracy above roughly 10 reps. Treat the number as a starting point, not a guarantee, and always lift within a safe range.
How the barbell plate calculator works
To load a bar to a target weight, subtract the bar weight from the target, then divide what's left between the two sides equally. The calculator loads each side greedily — heaviest plate first, then the next size down — until it reaches the per-side weight.
It uses standard plate sets: in pounds, 45, 35, 25, 10, 5, 2.5; in kilograms, 25, 20, 15, 10, 5, 2.5, 1.25. If the target can't be made exactly with those plates, it loads as close as it can and tells you how much is left over.
| Target | Bar | Per side |
|---|---|---|
| 225 lb | 45 lb | (225 − 45) ÷ 2 = 90 → 45 + 45 |
| 135 lb | 45 lb | (135 − 45) ÷ 2 = 45 → one 45 |
| 100 kg | 20 kg | (100 − 20) ÷ 2 = 40 → 25 + 15 |
Frequently asked questions
- How do I calculate my one-rep max?
- Take a set you can do with good form, then estimate your max from the weight and reps. The Epley formula is 1RM = weight × (1 + reps ÷ 30); this tool averages Epley and Brzycki for a balanced estimate.
- What is the Epley formula?
- It estimates one-rep max as 1RM = weight × (1 + reps ÷ 30). For a single rep it returns the weight itself; as reps rise the estimate climbs. So 100 lb for 5 reps gives about 117 lb.
- How accurate are 1RM estimates?
- They are rough estimates, not exact numbers. They are most reliable for sets of about 1–6 reps and become noticeably less accurate above roughly 10 reps. Use the figure as a starting point and adjust by feel.
- What weight should I use for sets of 5?
- A common guideline is about 85% of your one-rep max for sets of 5. The percentage table shows working weights for 1, 2, 4, 6, 8, 10 and 12 reps once you have an estimated 1RM.
- How do I load a barbell to a target weight?
- Subtract the bar weight from the target, split the remainder evenly between both sides, and load each side from the heaviest plate down. The plate calculator does this and flags when the exact weight can't be made.
- How much does a barbell weigh?
- A standard men's Olympic bar weighs 45 lb (about 20 kg). Women's Olympic bars are typically 35 lb (15 kg). This tool defaults to 45 lb, or 20 kg when you switch units.