One-Rep-Max Calculator — estimate your 1RM from reps (Epley & Brzycki)

How it works

Your one-rep max is the most weight you can lift for one full repetition of an exercise — the standard yardstick for strength and the basis most programs use to set training loads. Testing it directly means grinding out a true maximal attempt, which is fatiguing and, done carelessly, a way to get hurt. So the usual approach is to estimate it from a sub-maximal set: do a weight you can handle for a handful of clean reps, and a formula projects what a single all-out rep would have been.

This calculator uses the two equations the strength literature leans on most. Both take the same two numbers — the weight and the reps to fatigue:

• Epley (1985): 1RM = weight × (1 + reps ÷ 30)
• Brzycki (1993): 1RM = weight × 36 ÷ (37 − reps)

They agree closely and, in fact, cross at exactly ten reps, where both put your max at 1⅓ times the weight lifted. Below ten reps Epley reads slightly higher; above ten, Brzycki does. At one rep Brzycki returns the weight itself — sensible, since a single rep is your 1RM — while Epley sits about 3% above it. Neither is "the right one"; showing both frames the estimate as the range it really is.

Worked example

Take 100 kg lifted for 5 reps:

• Epley: 100 × (1 + 5 ÷ 30) = 100 × 1.1667 = 116.7 kg
• Brzycki: 100 × 36 ÷ (37 − 5) = 100 × 36 ÷ 32 = 112.5 kg

So your one-rep max is roughly 113–117 kg — a five-kilo spread that honestly reflects how much these projections can differ.

From that estimated max, the training-load table works backwards to show what to load for other rep targets, using load = 1RM ÷ (1 + reps ÷ 30). For the 117 kg Epley max: about 109 kg for 2 reps, 106 for 3, 100 for 5, 92 for 8, 88 for 10 and 83 for 12. Notice the 5-rep row comes back to the 100 kg you started with — the table is the same relationship read in reverse, so it lands exactly where you began.

Frequently asked questions

What is a one-rep max?

The heaviest load you can move for a single, technically sound repetition of a lift. It's the reference point for programming: most strength and hypertrophy plans prescribe work as a percentage of 1RM (say, "5 sets of 3 at 85%"), so knowing the number — even an estimate — turns those percentages into actual weights on the bar.

Should I use Epley or Brzycki?

Either — they're close, and the honest answer is a range rather than a single number. Epley reads a touch higher at low reps, Brzycki a touch higher above ten, and they meet at ten reps exactly. If you want one figure, average them; if you're programming, it's fine to use the lower of the two as the conservative choice.

Why won't it take more than 12 reps?

Because the formulas were built and validated on **low-rep sets** and lose accuracy as reps climb. Past about ten to twelve reps, the estimate drifts high and depends heavily on your muscular endurance rather than your true maximal strength. For the most reliable projection, use a weight you can lift for **two to six** clean reps.

How accurate is the estimate?

It's a projection, not a measurement. For a set in the low-rep range it's typically within a few percent of a tested max, but the real figure depends on the lift, your training age, technique and how close to failure the set actually was. Two people lifting the same weight for the same reps can have genuinely different true maxes. Treat the number as a well-founded starting point you refine with experience, not a certified result.

How do I turn my 1RM into training percentages?

Multiply. A load at *p* percent of your max is 1RM × p ÷ 100 — so 80% of a 117 kg max is about 94 kg. The training-load table on this page does the equivalent by rep target instead of percentage, since a given rep count corresponds to a rough percentage of 1RM (five reps ≈ 86%, ten reps ≈ 75%).

How should I test a set safely?

Warm up thoroughly, and pick a weight you're confident you can lift for the reps with **clean form** — a max estimate is only as good as the set behind it, and a sloppy or partial rep inflates it. Stop the set when your technique breaks down rather than pushing to true failure, use a spotter or safety pins for pressing and squatting movements, and build up gradually. This tool is a training aid, not medical or coaching advice; if you're new to lifting or returning from injury, get qualified guidance before testing heavy.