One Rep Max Calculator
Estimate your one rep max (1RM) using 7 proven strength formulas. Enter the weight you lifted and how many reps you completed. Works for bench press, squat, deadlift, overhead press, and any barbell lift. 100% private — nothing leaves your browser.
What Is One Rep Max (1RM)?
Your one rep max (1RM) is the maximum weight you can lift for a single repetition with proper form. It is the gold standard for measuring maximal strength and is used by coaches, athletes, and recreational lifters to program training intensity. Rather than attempting a dangerous maximal lift, you can estimate your 1RM mathematically from a submaximal set — for example, the weight you can lift for 3-10 reps.
Knowing your 1RM lets you calculate training percentages, track strength progress over time, and compare performance across different exercises. It is a foundational concept in strength training, powerlifting, and athletic performance programming.
How 1RM Formulas Work
This calculator uses seven well-established formulas to estimate your one rep max. Each formula uses a slightly different mathematical model — some are linear (Epley, O'Conner), while others use exponential decay (Mayhew, Wathen). The Epley formula (weight x (1 + reps/30)) is the most widely used in strength training literature. The Brzycki formula is popular in powerlifting circles and tends to give slightly lower estimates at higher rep ranges.
The 7 Formulas
Epley: weight x (1 + reps / 30)
Brzycki: weight x 36 / (37 - reps)
Lombardi: weight x reps^0.10
Mayhew: 100 x weight / (52.2 + 41.9 x e^(-0.055 x reps))
O'Conner: weight x (1 + reps / 40)
Wathen: 100 x weight / (48.8 + 53.8 x e^(-0.075 x reps))
Lander: 100 x weight / (101.3 - 2.67123 x reps)
By averaging all seven formulas, this calculator gives you a robust estimate that minimizes the bias of any single equation. The formulas agree closely for 1-6 reps and diverge more at higher rep ranges, which is why estimates above 10 reps carry more uncertainty.
Using 1RM for Training Programming
Once you know your estimated 1RM, you can program your training using percentage-based loading. For example: strength work typically uses 85-95% of 1RM for 1-5 reps, hypertrophy work uses 65-80% for 6-12 reps, and endurance work uses 50-65% for 15+ reps. Programs like 5/3/1, Texas Method, and Juggernaut Method all rely on accurate 1RM estimates.
Recalculate your 1RM every 4-8 weeks to adjust training loads as you get stronger. Many lifters use a "training max" of 90% of their estimated 1RM to build in a safety margin and ensure quality reps throughout a training cycle.
Strength Standards by Exercise
Strength standards help you understand where your lifts fall relative to the general population. They are based on body weight ratios — for example, an intermediate bench press is roughly 1.0x your body weight. Standards vary by exercise: squats and deadlifts have higher ratios because they recruit more muscle mass. These benchmarks are useful for goal-setting but should be treated as guidelines, not absolute rules.
Factors like training age, body composition, limb proportions, and gender all affect where you fall on the strength spectrum. The standards shown by this calculator are based on commonly referenced male ratios — female lifters can use roughly 60-70% of these values as equivalent benchmarks.
Tips for Safe Max Testing
If you choose to test a true 1RM in the gym, follow these safety guidelines: warm up thoroughly with progressively heavier sets, always use a competent spotter, use safety pins or a power rack, and never sacrifice form for weight. A good testing protocol is to work up in singles — for example, 70% x 1, 80% x 1, 90% x 1, then attempt your max.
For most lifters, estimating your 1RM from a 3-5 rep set is safer and nearly as accurate as a true max attempt. This calculator makes that process simple and instant.