How to Calculate Your One-Rep Max

7 min read · Updated September 26, 2026 · by the SolveCalcPro editorial team

Your one-rep max (1RM) is the most you can lift once with good form. Programmes often prescribe weights as percentages of it, but testing it directly is hard on the body. Estimating it from a lighter set is safer and nearly as useful. This guide shows how.

The main formulas

Epley: 1RM = w × (1 + reps ÷ 30). Brzycki: 1RM = w × 36 ÷ (37 − reps). Lombardi: 1RM = w × reps^0.10. O’Conner: 1RM = w × (1 + 0.025 × reps). Lifting 100 kg for 5 reps gives 116.7 kg (Epley), 112.5 kg (Brzycki), 117.5 kg (Lombardi) and 112.5 kg (O’Conner). The one rep max calculator averages six formulas: 115.8 kg.

How accurate are they?

They stay within a few kilograms of each other for moderate sets and drift apart above about 10 reps, where fatigue, technique and the exercise affect results more. The spread across formulas (here 112.5–119 kg on a 100 kg set) is a useful reminder that the answer is an estimate. For the best accuracy, use a heavy set of 3–8 reps taken to near failure with good form.

From 1RM to training weights

% of 1RM	Typical use
90–100%	Max strength, singles and doubles
80–90%	Strength, 3–6 reps
65–80%	Muscle building, 6–12 reps
50–65%	Warm-ups, technique, endurance

Reps possible at a given percentage vary by person and exercise; the calculator’s table shows typical values.

Safety first

Warm up progressively before heavy sets.
Use a spotter or safety bars for squats and bench presses.
Stop a set when form breaks down.
Do not test a true max when sleep-deprived, injured or alone.

Consider working with a qualified coach; organisations such as the American College of Sports Medicine publish exercise guidance. This guide is educational, not coaching or medical advice.

Practice questions

Test yourself, then tap to check. Answers are calculated by the tools linked below.

You squat 140 lb for 6 reps. What is your estimated 1RM?
Show answer
Estimated one-rep max (average of six formulas): 166.3 lb
A 28-year-old woman, 62 kg, 168 cm, lightly active, wants to maintain her weight. What are her BMR and TDEE?
Show answer
Daily calorie target: 1,882 kcal · Maintenance calories (TDEE): 1,882 kcal
Convert 12 stone to kilograms.
Show answer
12 st in kg: 76.20351816