Accurately estimate the heaviest weight you can lift for a single rep
A one-rep max calculator helps you estimate the heaviest weight you can lift without putting yourself through a risky max-effort test. This calculator uses established scientific formulas: Epley, Brzycki, Lander and Lombardi.
A few things worth knowing:
Picking the right weight is one of the most important decisions in every training session, and it directly affects how fast you build muscle and gain strength. That choice starts with your one-rep max: once you've estimated it with the calculator above, you can select the right percentage of it as your working weight based on your training goal.
The general rule is 85 to 95 percent of your one-rep max for 1 to 5 reps to build pure strength, 70 to 80 percent for 8 to 12 reps for muscle growth (hypertrophy), and 60 to 70 percent for higher reps to build muscular endurance. The training percentage table that appears on this page after you calculate lays out exactly what those weights are for you.
Before designing your programme, it's also worth understanding your body type and composition, since recovery capacity and response to training load vary from person to person. To get a clearer picture, try the body type test and the body fat percentage calculator.
Relative strength is your one-rep max divided by your body weight, and it is a far better measure than absolute strength for comparing athletes at different weights. The formula is simple: relative strength equals your one-rep max divided by your body weight. If your squat max is 120 kg and you weigh 80 kg, your relative strength is 1.5.
This figure matters most in sports like powerlifting, gymnastics, martial arts and explosive events, where an athlete has to control their own body weight and produce maximum force relative to their mass. Improving relative strength usually happens one of two ways: raising your one-rep max, or shedding excess body fat without losing muscle.
Because hydration and water weight can shift your daily body weight — and with it your relative strength figure — managing your daily water intake matters too. The daily water intake calculator can help with that.
A 1RM calculator is a free online tool that estimates your maximum strength scientifically from the weight and rep count you enter, rather than putting you through a risky and exhausting max-effort test. The calculator on this page draws on four established formulas — Epley, Brzycki, Lander and Lombardi — to give you the most accurate estimate for your training style and rep range.
The main advantage is safety and speed: no training partner needed, no injury risk, and two simple numbers give you both your one-rep max and a complete table of training percentages. That table lets you plan the weight for every set precisely according to your goal — strength, size or endurance — and progress consistently.