How to Estimate Your One-Rep Max

You don't have to test a max to know roughly where it is

Five clean reps at 225 puts your one-rep max somewhere around 255 to 265, depending on which published formula you ask.

That "depending on which one you ask" is the whole subject. Every 1RM formula is a curve fitted to how groups of lifters generally behave — not a measurement of you. So this calculator shows two of them rather than pretending there's one answer.

The two formulas

Epley: 1RM = weight × (1 + reps ÷ 30)

Brzycki: 1RM = weight × 36 ÷ (37 − reps)

At 225 × 5 reps:

• Epley: 225 × (1 + 5/30) = 225 × 1.1667 = 262.5
• Brzycki: 225 × 36/32 = 225 × 1.125 = 253.1

About nine pounds apart. Neither is wrong; they're different curves through roughly the same data.

They cross at exactly ten reps

This is the part that isn't in most write-ups, and it changes how you read the numbers.

Set the two formulas equal and solve:

(30 + r)/30 = 36/(37 − r) → r² − 7r − 30 = 0 → r = 10

An exact integer root. So:

Reps	Epley	Brzycki	Gap
1	232.5	225.0	7.5
5	262.5	253.1	9.4
10	300.0	300.0	0
15	337.5	368.2	30.7

Below ten reps Epley reads higher. Above ten, Brzycki does — which is the opposite of what you'll often see stated. And at exactly ten they agree to the decimal.

Why that matters

It's tempting to treat the gap between two formulas as a confidence measure — they agree, so it must be right.

At ten reps that reasoning fails completely. The gap is zero because the curves happen to intersect there, not because the estimate is good. A ten-rep set is a worse basis for a 1RM estimate than a three-rep set, and it's the one that looks most certain.

Trust a low-rep estimate with a moderate spread over a ten-rep estimate with none.

Use as few reps as you honestly can

Accuracy is best from 1 to 5 reps, where published comparisons put these formulas within a few percent of a tested max. It's still reasonable through 10, then degrades quickly.

The reason is straightforward: a high-rep set stops being a test of strength. At twelve reps you're measuring conditioning and how much discomfort you'll tolerate, and those vary between people far more than maximal strength does. Two lifters with identical maxes can be four reps apart at 70%.

The reps box stops at 15 for that reason. It's also worth noticing how Brzycki fails past its range — its denominator, 37 − reps, hits zero at 37 reps. The formula doesn't gradually get vaguer; it detonates. That's a useful reminder these are fitted curves, not laws.

The one place Brzycki is exactly right

At a single rep, Brzycki gives 36/36 = 1, returning exactly the weight you lifted. Which is correct by definition — a single rep is your max that day.

Epley's (1 + 1/30) adds 3.3% to a number that needs no adjusting.

Neither formula is broken. Brzycki's curve simply happens to be anchored correctly at that end.

Where these fit worst

The formulas were largely derived from bench press and squat data. They travel reasonably to most compound barbell lifts.

They fit deadlifts less well — many lifters manage fewer reps at a given percentage than the curves predict — and they fit isolation work and machines poorly. Treat the estimate as most trustworthy on the big compound lifts and as a rough guide elsewhere.

Don't go and attempt it

The number is an estimate from a curve fitted to other people. It assumes your reps were clean and close to failure. It knows nothing about your joints, your technique, or how today is going.

If you want to test a real max, that wants a proper warm-up progression, experience with the lift, and a spotter or safety bars — not a calculator's blessing.

What the estimate is genuinely good for is programming and tracking. Take it every few weeks under the same conditions and watch the line. A single reading has a few percent of error and moves with sleep and food; the trend across a block is the actual data.

Print the training max sheet and log the set each time rather than the estimate alone — the weight and reps are recoverable later, a bare number isn't.

Not medical or coaching advice. Attempting maximal lifts carries real injury risk. If you're new to a lift, returning from injury, or unsure, work with a qualified coach.

Sources: Arvo — 1RM formulas explained