One Rep Max Calculator

What is a one rep max calculator?

A one rep max calculator estimates your one-rep max (1RM) — the heaviest weight you could lift for a single repetition of an exercise — without you having to attempt a true maximal lift. You enter a weight you can handle for several reps and how many reps you completed, and the calculator predicts the equivalent single-rep load.

Testing a genuine one-rep max is demanding and carries a real risk of injury: form breaks down near the limit, and a failed lift without a spotter can be dangerous. Estimating your 1RM from a submaximal set gives you most of the same information from a set you can actually finish safely, which is why lifters and coaches rely on these formulas to gauge strength and set training loads.

How does it work?

Using the calculator takes three steps:

1. Enter the weight you lifted. Type the load you used for your set.

2. Enter the number of reps. Type how many clean repetitions you completed with that weight. The estimate is most accurate for sets of roughly 1 to 10 reps.

3. Choose a formula. Select Epley or Brzycki. Each is a slightly different curve fit to real lifting data, so they return close but not identical answers.

The calculator then returns your estimated 1RM. Because both formulas scale linearly with the entered weight, the result comes back in whatever unit you typed — there is no separate conversion step.

Formulas

Let $w$ be the weight lifted and $r$ the number of repetitions performed.

The Epley formula:

The Brzycki formula:

The Brzycki estimate climbs sharply as $r$ approaches 37 and is undefined at and beyond that point, so it is only meaningful for the moderate rep ranges these formulas are designed for. At a single rep ($r = 1$) both formulas return values close to the weight itself, and they diverge as the rep count rises — Brzycki is the more conservative of the two at higher reps.

Examples

• Example 1 (Epley): You lift 100 lb for 5 reps. Your estimated one-rep max is:

  $$1RM = 100\left(1 + \frac{5}{30}\right) \approx 116.7 \text{ lb}$$

• Example 2 (Brzycki): Using the Brzycki formula for the same 100 lb × 5 set:

  $$1RM = 100 \cdot \frac{36}{37 - 5} = 112.5 \text{ lb}$$

  Notice that Brzycki returns a lower estimate than Epley for the same set.

• Example 3 (Epley): You press 225 lb for 5 reps:

  $$1RM = 225\left(1 + \frac{5}{30}\right) = 262.5 \text{ lb}$$

Practical notes

• Keep reps moderate. These estimates are most reliable for sets of about 1 to 10 reps. A 20-rep set reflects your muscular endurance more than your maximal strength.

• Use clean reps only. Count only full-range repetitions completed with good form; partial or grinding reps distort the prediction.

• Treat it as a guide. Each formula is a prediction fit to other people’s data, so it may overestimate or underestimate your real max. Confirm important numbers cautiously and with a spotter.

FAQs

What is a one-rep max?

A one-rep max (1RM) is the heaviest weight you can lift for exactly one repetition of an exercise with good form. It is the standard benchmark for maximal strength.

Should I use Epley or Brzycki?

Epley is the most common default and the formula many gym apps use. Brzycki tends to be more conservative as the rep count climbs. Trying both gives you a useful range rather than a single point estimate.

Do I have to test a true max?

No. The point of this calculator is to estimate your 1RM from a submaximal set, so you can avoid the risk and fatigue of an all-out single.

Does it work for any lift?

Yes. The same formulas estimate the 1RM for the bench press, squat, deadlift, and other barbell lifts.