1RM Calculator (One-Rep Max)

What is a 1RM and why does it matter?

Your 1RM (one-rep max) is the heaviest weight you can lift for a single rep with proper form. It's the yardstick of strength training: every percentage in a program (8 reps at 70%, 4 reps at 85%, and so on) is defined relative to it. Without knowing your 1RM, load selection is guesswork — you either train too light or take unnecessary risks.

Why estimate instead of testing a true max?

A real 1RM attempt is technically demanding and carries injury risk even for experienced lifters. The good news: any set of 2–10 reps predicts your 1RM with 95%+ accuracy. This tool uses two established formulas side by side:

• Epley (1985): 1RM = weight × (1 + reps/30) — slightly more generous at higher rep counts.
• Brzycki (1993): 1RM = weight × 36 / (37 − reps) — very close to Epley at low reps, more conservative at high reps.

Example: 80 kg × 5 reps → Epley 93.3 kg, Brzycki 90 kg. Average: ~91.7 kg. Some disagreement between the formulas is normal; the average is a practical middle ground.

How to use training percentages

• Maximal strength: 85–95% → 2–6 reps, long rests (3–5 min).
• Hypertrophy (muscle growth): 65–80% → 6–12 reps. For the science of rep ranges, see how to build muscle.
• Strength endurance: 50–65% → 12+ reps, short rests.

The table this calculator produces shows your 60–95% loads with typical rep counts. When you plan your training week, the workout split guide is a good starting point.

Tips for an accurate estimate

• Use a set of 2–10 reps: above 12 reps the formula error grows noticeably.
• Take the set close to failure: "I did 5 but could have done 10" sets underestimate your 1RM.
• Estimate per exercise: your squat, bench press and deadlift maxes are independent — calculate each one. If your squat form is shaky, read the squat form guide first.
• Update regularly: recalculate every 4–6 weeks as you get stronger; training off an old 1RM slows progress.

Safety note: use a spotter on heavy sets and never trade form for load. This tool provides estimates; it is not medical or coaching advice.