What the one rep max calculator does
The one rep max calculator estimates the heaviest weight you could lift for a single repetition, based on a set you have already done. Instead of risking a true maximal attempt, you enter a submaximal set — say 225 lb for 5 reps — and the tool predicts your 1RM using the two most established equations, Epley and Brzycki. It then builds a percentage table so you can program your training loads without re-testing.
The two formulas
Epley: 1RM = weight × (1 + reps ÷ 30)
Brzycki: 1RM = weight × 36 ÷ (37 − reps)
Both were derived from real lifting data and agree closely at low rep counts. Epley drifts slightly higher as reps increase; Brzycki slightly lower. For a 5-rep set they typically land within a couple of percent of each other, which is why averaging them — as the headline number here does — is a sensible, balanced estimate.
Why fewer reps means a better estimate
These formulas were built from heavy, low-rep sets, so they are most accurate from about 2 to 8 reps. Once you go beyond 10 reps, muscular endurance starts to dominate over pure strength, and the prediction gets shaky — a person who can do 20 reps at a given weight might have a very different true max than the formula suggests. For the most reliable estimate, test with a hard set of 3 to 5 reps.
How to use the percentage table
Strength programs almost always prescribe load as a percentage of 1RM: maybe 5×5 at 80%, or a heavy single at 95%, or speed work at 60%. The table converts your estimated max into actual working weights at every 5% step, with rough rep guidance alongside. That lets you run programs like 5/3/1, Starting Strength progressions or any percentage-based block straight from your estimate.
Strength standards in perspective
One-rep maxes are personal, but rough benchmarks help. A common intermediate goal for the "big three" lifts is a bodyweight bench press, 1.5× bodyweight squat and 2× bodyweight deadlift, though these vary widely by sex, age, limb length and training history. Progress matters far more than comparison — track your estimated 1RM over months and aim for a steady upward trend.
Train safely
Estimating beats max-testing for most people, especially beginners. When you do lift heavy, use proper warm-up sets, sound technique and a spotter or safety pins for bench and squat. If a rep grinds to a stop or your form breaks, that rep does not count toward a clean estimate. Pair strength work with adequate protein — see the protein calculator — and enough calories to recover, via the calorie calculator.