One Rep Max Calculator

Estimate your one-rep max without maxing out

Your one-rep max (1RM) is the heaviest weight you can lift once with good form. Testing it directly is tiring and carries a higher injury risk. This one rep max calculator estimates it from a set you have already done — for example 100 kg for 5 reps — using seven published prediction equations, then averages them for a more balanced answer.

It works for most barbell, dumbbell or machine lifts, in kilograms or pounds. Below the result you get a percentage chart from 50% to 100% of your 1RM, rounded to loads you can actually make with standard plates, plus an RPE chart that turns a set at a given effort (RPE 6.5–10) into a percentage of your 1RM.

How to calculate your one-rep max

1. Do a hard set of 1–12 reps with good technique — ideally 3 to 8 reps for the most accurate estimate.
2. Enter the weight lifted and the reps completed, and choose kg or lb.
3. Read your estimated 1RM (the average of seven formulas) and compare the individual formula results.
4. Leave rounding on to round training loads to 2.5 kg or 5 lb, or switch it off for exact values.
5. Use the percentage table to pick loads for strength, hypertrophy or endurance work.

One Rep Max Calculator features

The 1RM formulas explained

Each equation predicts your maximum from the weight (w) and reps (r) of a submaximal set. They disagree slightly because they came from different lifters, so averaging smooths out the quirks of any single one.

Worked example: 100 kg for 5 reps gives 116.7 kg with Epley, 112.5 kg with Brzycki and 119.0 kg with Mayhew; the average of all seven is about 115.5 kg. At 80% of that, your working sets would use 92.5 kg after rounding.

• Epley: 1RM = w × (1 + r ÷ 30)
• Brzycki: 1RM = w × 36 ÷ (37 − r)
• Lombardi: 1RM = w × r^0.10
• Lander: 1RM = 100 × w ÷ (101.3 − 2.67123 × r)
• O’Conner: 1RM = w × (1 + 0.025 × r)
• Wathan: 1RM = 100 × w ÷ (48.8 + 53.8 × e^{−0.075 × r})
• Mayhew: 1RM = 100 × w ÷ (52.2 + 41.9 × e^{−0.055 × r})

Using percentages of 1RM to plan training

Most programmes prescribe weights as a percentage of 1RM. As a broad guide from the National Strength and Conditioning Association (NSCA): loads of about 85% or more for up to 6 reps build maximal strength, 67–85% for 6–12 reps suit muscle growth (hypertrophy), and 67% or less for 12 or more reps trains muscular endurance. Warm-up sets usually start around 40–60%.

The rep counts are averages: upper-body lifts and newer lifters often manage fewer reps at a given percentage. Use them as a starting point and adjust with how hard each set feels.

The protein calculator estimates daily protein needs and the weight converter handles other kg–lb conversions. Results are estimates, not professional training or medical advice.

RPE and percentage of 1RM

RPE (rating of perceived exertion) rates a set from 1 to 10, where 10 means no reps were left and 8 means about two. Reps in reserve (RIR) is the same idea: RIR = 10 − RPE. The chart follows the one popularised by Mike Tuchscherer of Reactive Training Systems: a set of 5 reps at RPE 8 is about 81.1% of 1RM, so 100 kg for 5 at RPE 8 suggests a 1RM near 123 kg. Reps 11–12 at the lowest RPEs go beyond the printed chart and are faded. These are population averages and approximations, not measurements.

Getting an accurate estimate

• Keep reps low. Estimates from 3–8 reps are more reliable than from 10–12, because fatigue and endurance play a bigger role in long sets.
• Use a true hard set. The set should finish at or very close to failure with clean technique — stopping with several reps in reserve underestimates your max.
• Stay safe. Use a spotter, safety pins or bumper plates for anything near maximal, and stop if form breaks down.