Advanced options
Estimates are most accurate from sets of 2 to 6 reps; the further from a true max effort, the wider the margin. Never attempt a max single without a proper warm-up, good technique and ideally a spotter.
What The One Rep Max Calculator Works Out
- Estimated one rep max: the heaviest weight you could lift once with good form, extrapolated from a hard set of 1 to 12 reps rather than tested directly. By default it averages the Epley and Brzycki formulas, which agree closely in the 2 to 10 rep range; 80 kg for 5 reps gives roughly 93 kg.
- Epley formula: weight x (1 + reps / 30). It tends to read slightly higher than Brzycki for sets above 10 reps.
- Brzycki formula: weight x 36 / (37 - reps). It is the formula most gym rep charts are built from and reads slightly lower at high reps.
- Percentage table: loads at 50% to 95% of your 1RM with the rep count each usually allows. Heavy strength work typically lives at 80% to 95% for 2 to 6 reps, hypertrophy work at 65% to 80% for 6 to 12 reps, and lighter technique or endurance work below that. Recalculate every few weeks and the table shifts up with you.
- Headline estimate uses (advanced): swap the average for a single formula, or for Lombardi (weight x reps^0.10) or O'Conner (weight x (1 + 0.025 x reps)), both of which are shown in their own card. Lombardi is popular for powerlifting; O'Conner is the most conservative at high reps.
- Round loads to (advanced): rounds every figure to what you can actually load. UK gyms usually have 1.25 kg as the smallest plate, so a 2.5 kg step per bar is the practical minimum; Olympic bars weigh 20 kg (15 kg women's bars).
- In the other unit (advanced): your 1RM converted between kg and lb (1 kg = 2.2046 lb), handy when a programme is written in the other unit.
- Load for your working set (advanced): the inverse of Epley: the weight at which your chosen rep count should be a true maximal set, shown with its percentage of 1RM.
- Strength to bodyweight (advanced): 1RM divided by your bodyweight. Common intermediate markers are around 1x bodyweight on the bench, 1.5x on the squat and 2x on the deadlift for men, with roughly two thirds of those ratios for women.
- Warm-up plan (advanced): a six-set ramp from the empty bar through 40%, 55%, 70%, 80% and 90% of 1RM to your working load, with reps falling as the weight rises. Estimates from sets above 10 to 12 reps are least reliable, and a predicted max is not a promise: build up gradually and use a spotter or safety bars. This is general fitness information, not medical advice.
Source and further reading: NHS: exercise guidelines.