1 Rep Max Formula: Estimate Your Maximum Lift

The 1-rep max (1RM) formula estimates the heaviest weight you could lift once, based on a weight you can lift for several repetitions. Enter the weight lifted and the number of repetitions completed to estimate your 1RM in the same units.

Formula

This calculator uses the Epley formula, a common way to estimate a one-repetition maximum from a multiple-repetition lift:

Estimated 1RM = weight lifted × (1 + repetitions ÷ 30)

• Weight lifted (w) is the load used for the set, in pounds (lb) or kilograms (kg).
• Repetitions (r) is the number of completed repetitions with that load.
• Estimated 1RM is the predicted maximum for one repetition, in the same weight unit as the input.

The calculation also shows the estimate as a percentage of the entered weight. The percentage is a comparison, not a second estimate of strength. If you enter kilograms, the result is in kilograms; if you enter pounds, it is in pounds. Convert the weight before calculating if you want a result in the other unit.

Worked Example

With the calculator’s default values, the lifted weight is 100 lb and the completed repetitions are 5.

1. Divide repetitions by 30: 5 ÷ 30 = 0.1667 (approximately).
2. Add 1: 1 + 0.1667 = 1.1667.
3. Multiply by the lifted weight: 100 × 1.1667 = 116.67 lb.
4. Rounded to one decimal place, the estimated 1RM is 116.7 lb.

The estimated 1RM is 116.7% of the 100 lb input weight. This is a prediction from the formula, not evidence that the lifter has actually completed a single repetition at 116.7 lb.

How the Estimate Works

A 1RM is the greatest load a person can lift once while completing the movement as intended. Since a true one-repetition test requires lifting that load, formulas estimate the maximum from a submaximal set instead. The Epley equation assumes that the number of repetitions completed relates to how much heavier a single-repetition load might be.

For example, using the same equation, a set of 8 repetitions at 60 kg gives 60 × (1 + 8 ÷ 30) = 76 kg. That estimate is not a universal conversion between eight repetitions and a particular percentage of 1RM; people differ in how many repetitions they can perform at a given relative load.

“One rep max” and “1RM” mean the same thing. The result is specific to the exercise and the conditions of the set. A bench-press estimate does not automatically predict a squat or deadlift maximum, and changing technique, range of motion, equipment, or fatigue can affect the comparison.

When to Use a 1RM Estimate

An estimated 1RM can help compare training performance over time without requiring a maximal single every time. It can also provide a reference for expressing training loads as percentages. For example, if an estimated squat 1RM is 120 kg, then 80% of that estimate is 96 kg. That arithmetic does not establish that 96 kg is appropriate for every set or lifter.

• Use a recent set from the same exercise you want to estimate.
• Count only repetitions completed with consistent technique and the intended range of motion.
• Compare estimates made under similar conditions, including equipment and exercise variation.
• Treat small changes cautiously: rounding, effort, rest, and daily performance can all affect the input.

Choosing Repetitions and Understanding Limits

Estimates tend to be more useful when they come from a challenging set of a few repetitions rather than a long set. As repetitions rise, muscular endurance and pacing may influence the result more, and the relationship assumed by the equation becomes less dependable. A set should still be performed with sound technique; there is no need to force extra repetitions just to obtain a calculation.

Different equations—including Brzycki and Lombardi—use different mathematical relationships and can produce different estimates from identical inputs. None can account fully for individual differences in strength, training history, exercise skill, or fatigue. The calculator uses Epley consistently so that its result is transparent and reproducible; it should not be read as a guaranteed maximum.

Do not enter a repetition count of zero: the estimate requires a completed set. Also avoid treating a result with many decimal places as more accurate than the underlying set. The displayed value is rounded to one decimal place, but the real-world uncertainty is usually greater than a tenth of a pound or kilogram.

Common Errors and Safe Use

One frequent mistake is mixing units—for example, entering a kilogram load while expecting a pound result. Another is entering the number of repetitions planned rather than the number actually completed. If the set includes incomplete repetitions, substantial assistance, or a different range of motion, it may not be comparable to a clean set in the same lift.

A calculated estimate is not a substitute for judgment about whether to attempt a heavy single. A direct 1RM test involves maximal effort and can carry risk, particularly with poor technique, inadequate preparation, or no appropriate safety setup. If testing a maximum, use suitable equipment and safeguards for the lift, and stop if technique breaks down or pain occurs. A calculator cannot assess readiness or make a lift safe.

Frequently Asked Questions

What is the formula for a 1 rep max?
The Epley formula is estimated 1RM = weight lifted × (1 + repetitions ÷ 30). It predicts a one-repetition maximum from a set performed at a lighter weight.

How do I calculate my 1RM from 5 reps?
Enter the weight you lifted for five completed repetitions. With Epley, multiply that weight by 1 + 5 ÷ 30, or about 1.167. The result is an estimate, not a confirmed single.

Is the Epley formula accurate?
It is a practical estimate, not an exact measurement. Accuracy varies with the lifter, exercise, repetition count, effort, and technique. A direct, properly conducted single is the actual result for that testing session.

Can I use this formula for kilograms?
Yes. Enter kilograms and the estimate will be in kilograms. The equation works the same way in pounds, provided you do not mix units.

Which 1RM formula is best?
No formula is best for everyone. Epley is widely used, while other equations may suit different repetition ranges or datasets. For consistent tracking, use the same equation and comparable sets each time.

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in w | Weight lifted | lb | 100 | 0
in r | Repetitions completed | reps | 5 | 1
out one_rm | Estimated 1-rep max | lb | w * (1 + r / 30) | 1
out percentage | Estimated 1RM as a percentage of lifted weight | % | one_rm / w * 100 | 1