One rep max calculator

Enter any weight and the reps you lifted it for — get your estimated 1RM and a percentage chart you can program with. No signup, works in kg or lb.

What is a one rep max?

Your one rep max (1RM) is the heaviest weight you can lift for a single rep with full range of motion and honest technique. It's the standard yardstick of strength — programs prescribe loads as percentages of it, and beating an old max is the clearest proof that training is working.

You don't need to test it under a bar. Because the relationship between load and reps is remarkably consistent, a hard set of 5 at 100 kg predicts a max around 117 kg — that's an estimated 1RM (e1RM), and it's how this calculator, and most modern training apps, measure strength week to week.

How the formulas work

The four estimates above come from published equations, each fitted to slightly different lifter populations:

• Epley — 1RM = weight × (1 + reps ÷ 30). The most common formula, and the one Liftrava uses for its in-app e1RM tracking.
• Brzycki — 1RM = weight × 36 ÷ (37 − reps). Nearly identical to Epley below 10 reps, more conservative above.
• Lombardi — 1RM = weight × reps^0.10. Gentler curve, popular for single-digit rep counts.
• O'Conner — 1RM = weight × (1 + reps ÷ 40). The most conservative of the four.

The headline number is the average of all four — in practice that lands within a few percent of a tested max for sets under 10 reps.

Using %1RM in your training

The percentage chart is where the number becomes useful. Strength work typically lives at 80–95% of 1RM (2–6 reps), hypertrophy work at 65–80% (7–12 reps), and lighter technique or endurance work below that. If your program says "squat 5×5 at 80%", the chart tells you exactly what to load.

One warning: your e1RM changes week to week — with sleep, bodyweight, and accumulated fatigue. Recalculate from recent sets rather than programming off a max you hit three months ago.