Brzycki 1RM Calculator

The Brzycki 1-Rep Max Calculator lets you estimate the maximum weight you could lift for a single repetition based on a lighter, multi-rep set — or reverse the calculation to find the bar load required for any rep count at a known 1RM. Both modes run entirely in your browser: no data is uploaded or stored anywhere.

How it works

The underlying equation is the Brzycki formula, derived by strength coach Matt Brzycki and published in the NSCA Strength and Conditioning Journal in 1993:

1RM = weight × 36 ÷ (37 − reps)

where weight is the load you actually lifted and reps is the number of clean repetitions you completed. Because the denominator (37 − reps) decreases as reps increase, the formula correctly reflects the fact that the higher the rep count you can complete at a given weight, the heavier your 1RM must be relative to that weight.

The inverse — solving for the load you need at a specific rep count — is:

weight = 1RM × (37 − reps) ÷ 36

This is what the “Required weight” mode computes: multiply your target or known 1RM by the reciprocal factor and you have your exact training load.

Why Brzycki and not another formula?

Dozens of 1RM prediction formulas exist. The most widely cited alongside Brzycki are Epley (weight × (1 + reps / 30)) and Lander (100 × weight / (101.3 − 2.67123 × reps)). All three are acceptable approximations for 2–10 reps. Brzycki’s linear form is particularly popular in powerlifting because it is intentionally conservative — it tends to predict a slightly lower 1RM than Epley, which reduces the risk of programming a weight that is actually beyond your capacity on a heavy single. This calculator shows Epley and Lander alongside Brzycki so you can see the full spread.

Worked example

A lifter completes a squat set of 5 reps at 120 kg:

1RM = 120 × 36 / (37 − 5)
    = 120 × 36 / 32
    = 120 × 1.125
    = 135 kg

From that 135 kg estimate the rep-max table shows:

So a hypertrophy block calling for 4 × 8 at 80% would mean loading the bar to 108–114 kg — information the calculator delivers in one click.

Accuracy and limitations

Brzycki’s formula is most accurate for 2–6 repetitions performed with genuine maximum effort. Accuracy decreases above 10 reps because muscular endurance becomes an increasingly large contributor to rep ceiling, and the linear model does not account for this. At very high rep counts (15+) any formula-based 1RM estimate should be treated as a rough guide only. The formula is also individual — highly trained powerlifters and those with fast-twitch dominant muscle fibre distribution often test higher than the formula predicts, while endurance-adapted lifters may test lower. Use the estimate as a starting point, not a substitute for an actual max attempt under safe conditions.

Using the training table in your programming

The rep-max training table is arguably more useful day-to-day than the headline 1RM figure. Strength coaches typically prescribe sets at a percentage of 1RM rather than at the absolute maximum:

• 90–100% (1–3 reps): neuromuscular max-effort work; used in peaking blocks close to competition.
• 80–90% (4–6 reps): classical strength zone; the basis of programmes like 5/3/1 and Texas Method.
• 70–80% (6–9 reps): high-threshold hypertrophy; builds cross-sectional area while maintaining tension.
• 60–75% (10–15 reps): moderate hypertrophy and work capacity; typical bodybuilding accessory work.

Once you have your Brzycki 1RM estimate you can read the exact bar load for any of these zones directly from the table — no further arithmetic needed. Round to the nearest sensible plate combination for practical loading.

Privacy

Every calculation runs locally in your browser using JavaScript. No weight, rep, or personal data is transmitted to any server. The page works fully offline once loaded.