One Rep Max Calculator

Your one rep max is the maximum weight you can lift for a single repetition with proper form. It serves as a benchmark for measuring strength and is used to calculate training loads. Rather than testing it directly (which carries injury risk), most lifters estimate it from a submaximal set.

No single formula is universally best. Epley and Brzycki are the most widely used and tend to agree closely at lower rep ranges (1-10 reps). Brzycki can be slightly more accurate for sets of 1-6 reps, while Epley tracks better at moderate rep ranges. For best results, compare multiple formulas and use the average as your working estimate.

Training percentages prescribe load relative to your 1RM. Strength programs typically use 85-100% of 1RM for 1-5 reps. Hypertrophy (muscle growth) programs use 65-85% for 6-12 reps. Endurance work uses 50-65% for 13-20+ reps. These zones help structure progressive overload across training cycles.

All 1RM formulas were developed using data from sets of roughly 1-10 reps. Above 10 reps, fatigue patterns, cardiovascular demand, and technique breakdown introduce error. A 20-rep set tests muscular endurance as much as raw strength, making the extrapolation to a single heavy rep unreliable.

Direct 1RM testing can be useful for powerlifters and competitive strength athletes, but it carries injury risk and requires significant recovery time. For most trainees, estimating 1RM from a 3-5 rep set is safer and practical. If you do test directly, always warm up thoroughly, use a spotter, and avoid grinding through reps with poor form.

Recalculate every 4-8 weeks as you progress, or whenever your training weights feel significantly easier or harder than prescribed. Strength gains happen faster for beginners (update monthly) and slow down for advanced lifters (update every 2-3 months). Track trends over time rather than reacting to single-session fluctuations.

The formulas estimate absolute 1RM based on the weight lifted and reps performed, regardless of body weight. However, relative strength (1RM divided by body weight) is a better comparison metric across different body sizes. A 100 kg squat means something different for a 60 kg lifter versus a 120 kg lifter.