Calculate Your 1RM: Formula, Examples and Limits

Calculate your one-repetition maximum (1RM), the heaviest weight you could lift once with proper technique, from a weight and the number of repetitions you completed. Enter the lifted weight in kilograms and the completed reps; the calculator estimates your 1RM using the Epley formula and also shows the equivalent in pounds.

Formula

The calculator uses the Epley formula: estimated 1RM = weight × (1 + repetitions ÷ 30). Here, w is the weight lifted in kilograms, r is the number of completed repetitions, and the output is an estimated one-repetition maximum in kilograms. The pound result converts that estimate using 1 kg = 2.20462 lb.

This is an estimate, not a measurement of a lift you actually performed. The formula is commonly used with a set of multiple repetitions to predict a single-rep maximum, but different equations can give different estimates.

Worked Example

Using the calculator’s defaults—60 kg for 8 repetitions:

1. Divide the reps by 30: 8 ÷ 30 = 0.2667.
2. Add 1: 1 + 0.2667 = 1.2667.
3. Multiply by the lifted weight: 60 × 1.2667 = 76.00 kg, rounded to two decimal places.
4. Convert to pounds: 76 × 2.20462 = 167.55 lb, rounded to two decimal places.

The estimated 1RM is therefore 76.00 kg (167.55 lb). It does not mean that the lifter has confirmed either weight in a one-repetition attempt.

How to Calculate Your 1RM

Use a set that you performed with a consistent range of motion and sound technique. Enter the load actually lifted and the number of repetitions completed—not the number you intended to do. For a barbell lift, include the bar’s weight in the total. For dumbbells, use the same convention each time, such as the weight of one dumbbell, and make sure any comparison uses that convention too.

• Choose a challenging set of roughly 2–10 repetitions for a more useful estimate. Estimates tend to become less dependable as the rep count rises, because muscular endurance increasingly affects how many repetitions someone can perform.
• Count only full, valid repetitions. Do not include partial reps, assisted reps, or repetitions completed with substantially different technique.
• Enter the load in kilograms. If your set was in pounds, convert first: pounds ÷ 2.20462 = kilograms. Alternatively, apply the same Epley formula directly in pounds; the predicted result will then be in pounds.
• Compare estimates only when the exercise, equipment, technique, and rep-count method are reasonably consistent.

For example, a set of 100 lb for 5 reps gives an Epley estimate of 116.67 lb: 100 × (1 + 5 ÷ 30). The calculator’s kilogram input does not change the underlying formula; it simply requires a unit conversion before entry.

What the Estimate Means

A 1RM is specific to a particular exercise and its rules of execution. Your estimated bench-press 1RM does not predict your squat 1RM, and a result from one squat variation may not transfer directly to another. It can be useful for tracking progress or choosing training loads without testing a maximum on every occasion.

Many training plans express a working weight as a percentage of 1RM. If an estimated 1RM is 100 kg, 70% corresponds to 70 kg. That arithmetic does not guarantee that 70 kg is appropriate for every set or person: fatigue, experience, exercise choice, and the plan’s intended effort all matter. Treat the estimate as a reference point rather than a promise about what you can lift on a given day.

Accuracy, Alternatives and Common Mistakes

No rep-based equation predicts everyone equally well. The Epley estimate may be reasonably useful for a hard, technically sound set at a moderate rep count, but it can be off because people differ in strength endurance, and because the set may not have been close to their true limit. A fresh one-rep test can give a direct result, but it is a different method and carries more practical risk than estimating from a submaximal set.

Other equations, including Brzycki and Lombardi, use different relationships between load and repetitions. They can produce different numbers from the same set; none turns a training set into an exact measurement. For instance, the Brzycki equation is often written as weight × 36 ÷ (37 − reps). Use one method consistently when comparing estimates over time instead of switching formulas to select the most flattering result.

• Using too many reps: A high-repetition set tests endurance as well as strength, making a single-rep prediction less certain.
• Entering the wrong load: Include the bar or other external load that was actually lifted; do not mix total weight with per-side weight.
• Rounding too early: Keep the original values through the calculation and round only the displayed answer. The calculator rounds its outputs to two decimal places.
• Confusing estimate with ability: A predicted number is not proof that you can safely lift it once. Daily readiness and technique can change performance.

Safety and Practical Use

You do not need to attempt a true maximum just to obtain a useful estimate. If you choose to test a single-rep maximum, use appropriate supervision and equipment for the lift, set up safely, and stop if technique breaks down or you feel pain. Do not treat a calculator result as a reason to attempt a load beyond your preparation. A submaximal set with good form is often the more practical input for an estimate.

Frequently Asked Questions

What is a 1RM?
A one-repetition maximum is the greatest load a person can lift once for a particular exercise while meeting the technique standard being used.

How do I calculate my 1RM from reps?
With the Epley formula, multiply the weight by 1 plus reps divided by 30. For example, 80 kg for 6 reps gives 80 × (1 + 6 ÷ 30) = 96 kg.

How accurate is a 1RM calculator?
It provides an estimate, not an exact result. Accuracy depends on the formula, exercise, rep count, effort, and how consistently the repetitions were performed.

Should I use kilograms or pounds?
Either unit works with the formula if the weight and result use the same unit. This calculator accepts kilograms and displays both kilograms and converted pounds.

Can I estimate my 1RM from 10 reps?
You can, but a prediction from a high-rep set may be less reliable because endurance affects the result more. A hard, well-executed set at a lower rep count is generally a more useful input.

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in w | Weight lifted | kg | 60 | 0
in r | Repetitions completed | reps | 8 | 1
out kg | Estimated 1RM | kg | w * (1 + r / 30) | 2
out lb | Estimated 1RM | lb | kg * 2.20462 | 2