1RM Calculator

A one rep max is the heaviest weight you can lift for a single clean repetition. Testing it for real is slow and hard on your joints, so almost every lifter estimates it instead: take a set you actually completed, and work backwards to the single you could have hit.

This calculator uses the Epley formula, the most widely used of these estimates:

1RM = weight × (1 + reps ÷ 30)

Worked example: you bench pressed 80 kg for 6 reps. That gives 80 × (1 + 6 ÷ 30) = 80 × 1.2 = 96 kg as your estimated bench press 1RM. In pounds the arithmetic is identical, since the formula is a ratio: 175 lb for 6 reps estimates a 210 lb max.

The table below shows what a 100 kg set converts to at each rep count, and what percentage of your one rep max that set represents. Scale it to your own numbers by multiplying: if you lifted 60 kg, multiply the middle column by 0.6.

The table starts at 2 reps on purpose. Epley is fitted for multi-rep sets, and at a single rep it returns 103.3 kg for a 100 kg lift. If you actually hit a clean single, that weight is your 1RM, no formula needed.

The number is only useful because of what you build on top of it. Once you have a max, every working set in a strength program is written as a percentage of it.

• 2 to 5 reps is the sweet spot. Estimates from this range typically land within 2 to 3 % of a tested max.
• Past 10 reps, accuracy falls apart. A high-rep set measures muscular endurance and work capacity as much as maximal strength, and Epley starts to overestimate badly.
• It varies by lift. Deadlift and squat estimates tend to run high, because those lifts fatigue you fast across a long set. Bench press estimates are usually the most reliable.
• It varies by athlete. Lifters with more fast-twitch dominance hit higher singles relative to their rep work, so their true max sits above the estimate.
• Take it to failure, or close. An estimate from a set you stopped 4 reps short is meaningless. Aim for 0 to 1 reps in reserve.

Epley is not the only option. Brzycki is the other formula you will see, and it reads:

1RM = weight ÷ (1.0278 − 0.0278 × reps)

The two agree closely up to about 6 reps, then diverge: Brzycki gives lower estimates on high-rep sets, Epley higher. For most people the difference is smaller than day-to-day variation in how strong they feel, so pick one and stay consistent. Consistency matters more than which formula, because what you actually track is the trend.