One Rep Max Calculator

A one rep max calculator estimates the heaviest weight you could lift once from a set of several reps. The Epley formula is 1RM = weight × (1 + reps ÷ 30), so 185 lb for 5 reps gives 185 × (1 + 5 ÷ 30) ≈ 215.8 lb. The average of seven published formulas for that same set is about 213.7 lb.

How to use the one rep max calculator

1. Choose pounds or kilograms.
2. Enter the weight you lifted and the number of clean reps you completed in one set, taken close to failure.
3. Read the estimated one-rep max (1RM). By default it is the average of seven formulas. You can pick a single formula instead.
4. Check the table of all seven estimates to see how far apart they are.
5. Use the percentage table to plan training loads. Round them to the plates you have, and open Show steps to see every formula worked out.

What a one-rep max is

Your one-rep max is the most weight you can lift for one complete repetition of an exercise with good form. It is specific to each lift, so your bench press 1RM tells you nothing exact about your squat. Coaches use it to set training loads as a percentage, for example 3 sets of 8 at 75% of 1RM.

Testing a true 1RM means working up to a single all-out lift, which takes time and carries more risk. Estimating it from a lighter set that you take close to failure is the more common way to get the number.

One rep max formulas

In each formula, w is the weight lifted and r is the number of reps completed. The result is in the same unit as w, pounds or kilograms.

Epley and O’Conner are straight lines: each extra rep adds a fixed share of the weight. Brzycki and Lander divide by a number that shrinks as reps go up, so their estimates rise faster at high reps. Wathen and Mayhew use an exponential curve, and Lombardi uses a power of the reps. The Wathen equation is sometimes misspelled “Wathan”. The original author is Dan Wathen, writing in the NSCA’s Essentials of Strength Training and Conditioning.

When you enter 1 rep, the calculator returns the weight itself. A single rep already is a one-rep max, and the formulas are meant for sets of 2 or more reps.

One rep max examples

Example 1: 185 lb for 5 reps

Epley: 185 × (1 + 5 ÷ 30) = 185 × 1.1667 ≈ 215.8 lb. Brzycki: 185 ÷ (1.0278 − 0.139) = 185 ÷ 0.8888 ≈ 208.1 lb. Lombardi: 185 × 5^0.10 ≈ 185 × 1.1746 ≈ 217.3 lb. The other four give 208.1, 215.7, 210.4 and 220.2 lb. The average of all seven is about 213.7 lb, with a spread of about 12 lb between the lowest and highest estimates.

Example 2: 100 kg for 8 reps

Epley gives 100 × (1 + 8 ÷ 30) ≈ 126.7 kg. Brzycki gives 100 ÷ (1.0278 − 0.2224) = 100 ÷ 0.8054 ≈ 124.2 kg. O’Conner gives 100 × 1.2 = 120.0 kg. At 8 reps the formulas disagree by almost 8 kg, which is why the average is a sensible middle value.

Example 3: planning a training load

Say your estimated 1RM is 213.7 lb and your program calls for 80%. Multiply the unrounded estimate: 0.80 × 213.66 ≈ 170.9 lb, which rounds to 170 lb with 5 lb plates. Brzycki’s relationship suggests about (102.78 − 80) ÷ 2.78 ≈ 8 reps at that load.

Percentage of 1RM chart

Brzycki’s formula can be rearranged into a percentage: %1RM = 102.78 − 2.78 × reps. The table shows what it predicts for 1 to 10 reps. The percentage table in the calculator runs it the other way, turning a percentage into an approximate number of reps.

These are averages. Some people can do many more reps at 75% than others, and the number changes from one exercise to another.

How accurate is a one rep max estimate?

Studies that compare these formulas with tested maxes find that they work best with low reps. A 2024 study by Ribeiro and colleagues in the International Journal of Strength and Conditioning reports that the equations are more accurate when about 3 to 5 reps are performed and less precise above 10 reps. In that study, Lombardi was the most accurate for men in the bench press and squat, while for women several equations, including Brzycki and Lander, matched the tested values in those lifts.

An earlier study by LeSuer and colleagues (1997) tested seven equations in the bench press, squat and deadlift. As summarized by Eston and Evans (2009), all seven underestimated the deadlift 1RM by an average of 9 to 14%. So treat the result as a range, not one exact number. The calculator shows the lowest and highest estimates for that reason.

Testing a one-rep max safely

An estimate from a set of 3 to 10 reps is the lower-risk way to get the number. If you or your coach decide to test a true max:

• Have a trained spotter or coach supervising, and use safety bars or pins for squats and bench presses.
• Warm up well and work up in small jumps, resting fully between heavy singles.
• Stop if your form breaks down or anything hurts.
• Beginners should learn the technique first. Anyone with an injury, heart condition or other health concern should get advice from a doctor first.

This calculator gives estimates for planning training. It is not medical advice.

Common one rep max mistakes

• Counting reps from several sets. Use the reps from one set only.
• Using a set that was not close to failure. If you stopped with several reps left, the estimate will come out too low.
• Using very high reps. Above 10 reps the formulas drift apart. A heavier set gives a better estimate.
• Counting sloppy reps. Bounced or partial reps make the estimate too high.

Sources

Checked November 2026.

• Ribeiro AS, et al. Accuracy of 1RM prediction equations before and after resistance training in three different lifts. International Journal of Strength and Conditioning. 2024;4(1) (Table 1 lists the Brzycki, Lander, Lombardi, Mayhew, O’Connor and Wathen equations)
• Marzagao T. A weight-dependent 1RM prediction equation optimized on 303,494 near-failure sets across 388 exercises. arXiv preprint (states the Epley, Brzycki, Wathen and Mayhew equations with their original references)
• Lacio ML, et al. Precision of 1-RM prediction equations in non-competitive subjects performing strength training. Motricidade. 2010;6(3):31-37 (O’Conner, Lander and Brzycki %1RM equations)
• Eston R, Evans HJL. The validity of submaximal ratings of perceived exertion to predict one repetition maximum. J Sports Sci Med. 2009;8:567-573 (summarizes LeSuer et al. 1997)

The original formula sources are: Epley B (1985), Poundage Chart, Boyd Epley Workout. Brzycki M (1993), J Phys Educ Recreat Dance 64(1):88-90. Lombardi VP (1989), Beginning Weight Training. O’Conner B, Simmons J, O’Shea P (1989), Weight Training Today. Wathen D (1994), Load assignment, in Essentials of Strength Training and Conditioning. Lander J (1985), NSCA Journal 6:60-61. Mayhew JL, et al. (1992), J Appl Sport Sci Res 6:200-206.

One rep max practice quiz: 10 questions

Test yourself with 10 multiple-choice questions. Choose an answer and press Submit to see if you are right and why. Your score appears at the end.

Frequently asked questions

How do you calculate your one rep max?

Do one set to near failure with good form, then put the weight and reps into a formula. With Epley, 1RM = weight × (1 + reps ÷ 30). For 200 lb × 6 reps that is 200 × 1.2 = 240 lb.

Which one rep max formula is most accurate?

No single formula wins for every lift and every person. Studies find different winners for different groups, so averaging several formulas, as this calculator does by default, is a practical middle ground.

Is it safe to test your one rep max?

A true max attempt is the riskiest set in training. Do it only with a trained spotter or coach supervising, after a full warm-up, and with safety equipment. Estimating from a set of 3 to 10 reps avoids the all-out lift.

How many reps can I do at 80% of my 1RM?

Brzycki's relationship predicts about (102.78 − 80) ÷ 2.78 ≈ 8 reps. Real numbers vary by person and exercise, so use it as a starting point.

Does the formula change for kilograms?

No. Every formula multiplies or divides the weight by a number that depends only on reps, so it works the same in pounds or kilograms. To convert, 1 lb = 0.45359237 kg.

Related calculators

• Percentage calculator to find any percent of your 1RM
• Percent change calculator to track strength gains
• Unit converter for pounds and kilograms
• Descriptive statistics calculator to average and compare several estimates