One Rep Max (1RM) Calculator

This one rep max calculator estimates your one-repetition maximum from a completed set using the Epley, Brzycki, and Lombardi formulas. Enter the weight you lifted and the reps you completed, choose pounds or kilograms, and the calculator returns an estimated 1RM you can use for training percentages and progress checks.

$\text{Epley 1RM} = \text{weight} \times (1 + 0.0333 \times \text{reps})$

The Brzycki result is:

$\text{Brzycki 1RM} = \text{weight} \times \frac{36}{37 - \text{reps}}$

The Lombardi result is:

$\text{Lombardi 1RM} = \text{weight} \times \text{reps}^{0.1}$

Each result is rounded to two decimal places. Epley adds a fixed percentage for each repetition. Brzycki uses a fraction that rises as repetitions increase. Lombardi uses a power function, which often sits near Epley for common lower-rep examples but can diverge depending on reps.

Use a consistent observed set

Record the exercise, entered load, unit, and repetitions together with the estimate. Compare repeated observations only when their exercise and counting basis match. Do not infer a strength change from switching units or comparing different lifts. The result is an estimate from the supplied set, not an instruction to attempt that load or a safety assessment for a maximal effort.

Worked example

Suppose you lift 135 lb for 5 repetitions. The Epley estimate is:

$135 \times (1 + 0.0333 \times 5) = 157.4775$

Rounded like the calculator, that displays as 157.48 lb. Brzycki is:

$135 \times \frac{36}{37 - 5} = 151.875$

That displays as 151.88 lb. Lombardi is:

$135 \times 5^{0.1} = 158.5709$

That displays as 158.57 lb. The copy text would summarize the same three estimates in the selected unit. If you enter kilograms instead, the arithmetic is identical and the labels change to kg.

Interpreting an estimated max

A calculated 1RM is most useful as a consistent yardstick. If your Epley squat estimate rises from 140 kg to 150 kg using the same depth and similar rep range, that likely reflects progress even if you never test a true single. Strength coaches often prescribe work sets as percentages of a max or estimated max, but the estimate should be adjusted for the day. Poor sleep, illness, a hard previous session, or a new exercise variation can make a normal percentage feel unusually heavy.

ACSM physical-activity guidance supports resistance training as part of adult fitness, but it does not mean maximal attempts are necessary for everyone. Many people can build strength with submaximal sets, progressive overload, and good technique. If your goal is body composition rather than max strength, compare this estimate with the body fat calculator or calorie calculator to keep strength progress in context.

For programming, use the estimate conservatively. A set of five done after several warm-up sets may predict differently than a fresh set of five. A paused bench press, touch-and-go bench press, dumbbell press, and machine press should each have their own history. The cleaner your input set is, the more useful the trend becomes.

Choosing inputs

Use a recent set from the same lift you want to estimate. If the set was stopped with many reps in reserve, the calculator will underestimate your current max because the rep count does not represent a hard effort. If the set used bouncing, altered depth, straps on one attempt but not another, or an unusually long rest, write that context down. Consistency makes the estimate more useful than chasing the largest possible number.

Common mistakes

• Entering a set with sloppy calculator, shortened range of motion, or help from a spotter.
• Using a high-rep endurance set and treating the estimate as equally reliable as a lower-rep strength set.
• Mixing exercises. A leg press 1RM estimate is not a squat 1RM estimate.
• Assuming the highest formula is the correct one because it is more exciting.
• Attempting the predicted number without a progressive warm-up, safeties, or spotting.

Limitations and health disclaimer

This calculator provides general educational fitness information only. It is not medical advice, coaching supervision, or a clearance to attempt maximal lifting. Stop if you have pain, use appropriate equipment, and seek qualified professional guidance if you are new to heavy resistance training, returning from injury, or managing a health condition.

Sources

• ACSM, Physical Activity Guidelines — resistance-training context within adult activity guidance.

• CDC, Adult physical activity basics — public-health guidance including muscle-strengthening activity.

• WHO, Physical activity — global recommendations for activity and health.

• 16937972 — Peer-reviewed evaluation of Epley, Brzycki, and Lombardi one-repetition-maximum prediction equations from multiple-repetition testing.