Estimate your one-rep max from the weight and reps of a set, with four formulas and a table of percentages.
A one-rep max (1RM) is estimated by putting the weight and the number of reps you did into a formula, so you do not have to attempt a single maximal lift. This page uses four published formulas: Epley (1985), 1RM = weight × (1 + reps ÷ 30); Brzycki (1993), weight × 36 ÷ (37 − reps); Lombardi, weight × reps^0.10; and O'Connor, weight × (1 + 0.025 × reps). The default example is 100 kg for 5 reps. Epley gives 116.7 kg, Brzycki 112.5 kg, Lombardi 117.5 kg and O'Connor 112.5 kg, and their average is 114.8 kg. The average is the headline number because no single formula is known to be best, and the four rarely agree exactly. With one rep the weight itself is the max, so the page shows it as the result and does not apply the four formulas, which are meant for 2 or more reps. Whole reps from 1 to 30 are accepted, and weights up to 2000.
Below the answer is a table from 100% down to 50% in steps of 5. Each weight is the average 1RM times the percentage, so at 114.8 kg, 90% is 103.3 kg and 80% is 91.8 kg. The reps column shows how many reps that percentage usually allows, found by solving the Brzycki formula for reps: reps = 37 − 36 × percentage ÷ 100, rounded and never below 1. That makes 95% about 3 reps, 85% about 6, 75% about 10 and 50% about 19. Because the weights come from the average and the reps from Brzycki alone, a row will not match your own set exactly; it is a planning guide for choosing a load, not a promise.
These formulas say most about sets of a few reps. The further you go beyond 10 reps, the less a single set tells you about a heavy single, because fatigue and conditioning start to decide the set, so the page adds a warning above 10 reps. Brzycki cannot be used at 37 reps or more, which is why the page stops at 30. The estimate also depends on the lift: a bench press, a squat and a deadlift do not scale the same way, and technique, sleep and warm-up change the result from day to day. A set taken to true failure with a spotter gives a better estimate than a set that stopped when it felt hard. Nothing here is coaching or medical advice; it is arithmetic on the numbers you type.
Use the estimate to pick working weights, not to decide what to lift on a test day. If a coach programmes a set at 80% of your max, read the 80% row; if you are comparing two lifters, use the same formula for both. Switching between kg and lb changes the labels, not the maths: type the weight in the unit you lifted it in and the table comes back in that unit.
Put the weight and reps into a formula. For 100 kg × 5 reps, Epley is 100 × (1 + 5 ÷ 30) = 116.7 kg, Brzycki is 100 × 36 ÷ 32 = 112.5 kg, and the page averages four formulas to 114.8 kg. Type your own set and the working appears under the answer.
Epley is 1RM = weight × (1 + reps ÷ 30). With 80 kg for 8 reps that is 80 × (1 + 0.2667) = 101.3 kg. It was published in 1985 and is applied here to 2 or more reps; for 1 rep the weight itself is the max and Epley is not applied.
Brzycki is 1RM = weight × 36 ÷ (37 − reps). With 60 kg for 10 reps that is 60 × 36 ÷ 27 = 80 kg. At 37 reps the divisor is zero, so the formula cannot be used, and this page stops at 30 reps.
They are curves fitted by different people, and they grow differently with reps. At 100 kg for 10 reps, Epley and Brzycki both give 133.3 kg, Lombardi gives 125.9 kg and O'Connor 125.0 kg. The average smooths that spread.
It gets rougher as reps rise. A set of 3 to 5 reps says more about a heavy single than a set of 20 does, and the page warns above 10 reps. It is an estimate, and a real max varies from day to day.
No. The calculation runs in your browser and the numbers stay in this tab. They are not uploaded or stored on your device. Reloading the page puts the example back. The page only counts that a result was shown, without any of your numbers.