One Rep Max Calculator
Estimate your one-repetition maximum (1RM) for any lift from a submaximal set.
The Formula
1RM = Weight × (1 + Reps / 30)
Brzycki Formula:
1RM = Weight × 36 / (37 − Reps)
Epley: 100 × (1 + 5/30) = 100 × 1.167
= 117 kg estimated 1RM
Brzycki: 100 × 36 / (37−5) = 112.5 kg
What Is a One Rep Max?
Your one-repetition maximum (1RM) is the maximum amount of weight you can lift for exactly one repetition with proper form. It is the standard measure of absolute strength in powerlifting and strength sports, and it is widely used to set training intensities across all rep ranges. Rather than attempting a true maximal lift — which carries injury risk, especially for less experienced lifters — most athletes use a submaximal set (a set of multiple reps at a challenging but manageable weight) and plug those numbers into a formula to estimate their 1RM.
1RM Formulas: Which One to Use?
Several formulas estimate 1RM from submaximal performance, and each produces slightly different results. The most commonly used are: the Epley formula (Weight x (1 + Reps/30)), the Brzycki formula (Weight x 36/(37 - Reps)), and the Lander formula ((100 x Weight)/(101.3 - 2.67123 x Reps)). All three are most accurate for sets of 1–10 reps — accuracy decreases significantly at higher rep counts (15+). Our calculator shows all three alongside an average for comparison.
How to Use Your 1RM for Programming
Once you know your estimated 1RM, you can calculate training weights for different rep ranges and goals. Strength work (1–5 reps) is typically done at 85–100% of 1RM. Hypertrophy work (6–12 reps) at 67–85%. Muscular endurance (12+ reps) at 65% and below. Progressive overload — gradually increasing the weight, reps, or volume over time — is the fundamental driver of strength and muscle gains. Recalculate your 1RM every 4–8 weeks to keep your training percentages accurate as you get stronger.
Frequently Asked Questions
How accurate are 1RM estimation formulas?
1RM formulas are most accurate for 1–10 rep sets performed to near-failure. Accuracy is typically within 5–10% when used correctly. The formulas become progressively less reliable at higher rep counts because endurance factors start to influence performance more than pure strength. If your last set was 15 reps, the estimate is an educated guess at best.
What percentage of 1RM should I train at for different goals?
For maximal strength (1–3 rep sets): 90–100% of 1RM. For strength and power (3–5 reps): 80–90%. For muscle hypertrophy (6–12 reps): 67–85%. For muscular endurance (12+ reps): 65% and below. Most well-rounded strength programs incorporate multiple rep ranges and percentages across a training week or training block.
Should beginners test their 1RM?
Generally no. Beginners benefit more from learning proper technique with moderate weights than from maximal efforts. True 1RM testing requires excellent technique and neural efficiency developed through months of consistent training. A submaximal set at a challenging weight (leaving 1–2 reps in reserve) is a safer way for newer lifters to estimate strength without the injury risk of a true max attempt.
How often should I test my 1RM?
Most intermediate and advanced lifters test or retest 1RM every 8–16 weeks — typically at the end of a training block. More frequent testing is unnecessary and adds fatigue without training benefit. For programming purposes, recalculating estimated 1RM from a challenging training set every 4–6 weeks is more practical and lower risk than formal maximal testing.
Does 1RM differ between individuals at the same body weight?
Yes, significantly. Factors that affect 1RM beyond body weight include muscle fiber type distribution (more fast-twitch fibers favor strength), limb proportions (shorter limbs create better mechanical advantage for some lifts), training history, neural efficiency, technique, and genetics. A 200-pound recreational lifter and a 200-pound competitive powerlifter can have dramatically different 1RMs — this is largely a reflection of training specificity, not just raw muscle mass.