One-Rep Max (1RM) Calculator

Pick a recent working set taken close to failure with clean technique: the last rep should have been hard, with perhaps one more rep possible at most. A set stopped well short of failure makes both formulas underestimate.

Enter the weight lifted (100) and the reps performed (5). The calculator has no unit switch; the answer comes back in whatever unit you entered.

Read the three estimates. Epley 116.7, Brzycki 112.5, and the highlighted average 114.6. A 4.2 kg gap at five reps is small, so the average is a sensible working number.

Use the percentage table, which is built from the average. For this lifter, 90% is 103.1 kg, 85% is 97.4 kg, 80% is 91.7 kg, 75% is 85.9 kg and 70% is 80.2 kg. A program calling for sets of five at 80% means about 91.7 kg, which you would round to the nearest plates you have: 92.5 kg, or 90 kg on a heavy day.

Re-enter a fresh set every few weeks. The estimate is only as current as the set behind it.

Epley: 1RM = w × (1 + r ÷ 30). Attributed to Boyd Epley's 1985 strength-training poundage tables. Each extra rep adds one-thirtieth of the lifted weight.

Brzycki: 1RM = w × 36 ÷ (37 − r). Published by Matt Brzycki in the *Journal of Physical Education, Recreation & Dance* in 1993 as a way to predict a 1RM from reps to fatigue.

Average = (Epley + Brzycki) ÷ 2, and each table row = Average × percentage, for 95% down to 50% in steps of 5.

Input handling: reps are held between 1 and 20. At exactly 1 rep both estimates equal the weight lifted, so 140 kg for a single returns 140 kg rather than Epley's 144.7. Above 20 reps the calculator uses 20. A negative weight is treated as 0.

Where the formulas agree and part ways: below 10 reps Epley gives the higher estimate; at exactly 10 reps they are identical (100 kg × 10 gives 133.3 from both); above 10 Brzycki climbs faster, because its denominator shrinks toward zero as reps approach 37. At 60 kg × 15, Epley says 90.0 and Brzycki 98.2, an 8.2 kg disagreement on a 60 kg set.

Enter 225 and 8. Epley returns 285.0 lb, Brzycki 279.3 lb, and the average is 282.2 lb. The gap is now 5.7 lb, wider than at five reps, which is the formulas telling you the set was further from a single.

The table gives 90% at 253.9 lb, 80% at 225.7 lb and 70% at 197.5 lb. The 80% row is essentially the weight this lifter just used for eight, which is a useful cross-check: the formulas say eight reps sits a little under 80% of a maximum.

You can read that relationship straight off the equations. By Epley, a set of 10 reps is done at 1 ÷ (1 + 10/30) = 75% of 1RM and a set of 5 at about 86%; by Brzycki, 10 reps is also 75% and 5 reps is about 89%. So a program that asks for sets of ten at 75% is asking for a genuine near-failure set, not an easy one.

A true max attempt is a skill as much as a test. It needs practised technique under heavy load, a proper warm-up progression, and a spotter or safety bars set at the right height. Estimating from a submaximal set is the better choice for beginners still learning a lift, anyone returning from injury, anyone training alone without safeties, during a fatigued block of training, and for lifts that are hard to bail out of safely. Anyone with a cardiovascular condition or who is pregnant should get medical advice before maximal efforts.

Accuracy depends mostly on reps. Brzycki presented his equation for sets of up to about ten repetitions, and estimates from low-rep sets of a few reps generally sit closer to a real single than estimates from long sets. Past ten, endurance rather than strength sets the rep count, and people with the same 1RM can differ widely in how many reps they manage at 70%. Treat any estimate from a set of 12 or more as a rough range, and look at the Epley-Brzycki gap as a warning light.

Estimates also vary by lift. The equations were developed with multi-joint barbell lifts in mind; for isolation exercises and machines the rep-to-load relationship can differ, so use the result for programming, not for comparing yourself with lifting standards.

Both formulas are general equations, not a model of you. They do not account for training age, muscle fibre make-up, technique breakdown near failure, or whether the set really went to failure. Reps in reserve inflate or deflate the result directly: a set of five with two reps left over is really a seven-rep effort.

The calculator does not know the unit, the exercise, or your equipment. It is not a safety assessment and cannot tell you whether a weight is safe for you to attempt. If you have a medical condition, injury or are pregnant, speak to a doctor before heavy lifting, and always use a spotter or safety equipment for near-maximal sets.

An estimated 1RM is most useful inside a plan: the Workout Calculator structures sets and weekly volume around the percentages above. Strength gains need energy and protein, so the TDEE Calculator estimates daily calorie needs and the Macro Calculator turns that into protein, carbohydrate and fat targets. To see how the number compares with typical lifters of your bodyweight, use the Bench Press Standards Calculator and the Squat & Deadlift Standards Calculator. For equipment-free benchmarks, the Push-Up & Sit-Up Fitness Test Calculator rates muscular endurance, and the Grip Strength Standards Calculator compares a dynamometer reading with age and sex reference bands.