How accurate are 1RM calculators?

1RM estimates are generally accurate to within ±5–10% of your actual maximum when based on 1–10 reps. Accuracy decreases as rep count increases — estimates from sets of 1–5 reps are more reliable than those from sets of 10+. Factors like fatigue, exercise selection, and individual muscle fibre composition also affect accuracy.

What weight and reps should I use for the most accurate result?

For best accuracy, use a weight you can lift for 3–8 reps with good form but would struggle to complete more than 10. Avoid very high rep sets (12+) as the formula accuracy declines. A set taken to near-failure gives a better estimate than a set performed well within your capacity.

How do I use the 1RM percentage table?

The percentage table shows training loads for different goals. 90–100% is used for maximal strength testing and competition. 80–85% is typical for strength training (3–5 reps). 70–80% is used for hypertrophy (6–12 reps). 60–70% is used for muscular endurance and volume work. Programming your training based on percentages of your 1RM allows progressive overload to be tracked objectively.

Which 1RM formula is most accurate?

No single formula is universally best. The Epley and Brzycki formulas are the most widely used and perform well for most people at moderate rep ranges. The Mayhew formula tends to perform better at higher rep ranges. Using the average of all five formulas, as this calculator does, gives the most balanced and reliable estimate.

How often should I re-test my 1RM?

Testing your 1RM directly carries injury risk and is taxing on the nervous system. Most athletes recalculate their 1RM using the calculator every 4–8 weeks after a new working set, rather than attempting a true max lift. Formal maximal testing is typically reserved for powerlifting or strength competitions.

One Rep Max (1RM) Calculator

Calculate your maximum strength for any lift using 5 validated scientific formulas. Get a full percentage-based training table to programme your workouts with precision.

Weight Lifted (kg)

Reps Completed

1–30 reps for accuracy

What is a One Rep Max (1RM)?

Your One Rep Max (1RM) is the maximum weight you can lift for a single repetition of a given exercise. It is the universal standard for measuring strength and is widely used to programme resistance training loads.

Rather than attempting a dangerous true maximum, this calculator estimates your 1RM from a submaximal lift — a weight you can perform for 2–10 reps with good form. Simply enter the weight and reps, and the calculator applies five validated formulas to estimate your maximum.

The five formulas used are Epley (1985), Brzycki (1993), Lander (1985), Lombardi (1989), and Mayhew (1992). Each formula weights the relationship between load and reps slightly differently, so the average of all five provides the most reliable estimate. The resulting percentage table lets you programme your training zones directly — from 60% for volume work up to 95% for near-maximal strength sets.

Frequently Asked Questions

A one rep max (1RM) is the maximum amount of weight you can lift for exactly one repetition of an exercise with proper form. It is used as a benchmark for strength and to calculate appropriate training loads. For example, if your 1RM squat is 100 kg, you would typically train at 70–85% (70–85 kg) for strength and hypertrophy work.

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