The Brzycki Formula Explained: How Accurate Is Your Predicted 1RM?

The Brzycki formula is one of the two most widely used methods for estimating a one-rep max (1RM) from a lighter set taken to, or near, failure. It was developed by strength coach Matt Brzycki and published in a 1993 fitness journal article as a simpler alternative to earlier prediction equations. Today it sits behind most 1RM calculators, including the one on this site. This guide explains exactly how the formula works, walks through worked examples, and looks honestly at how accurate the prediction is against a real, tested max.

The formula

1RM = weight × 36 / (37 − reps)

Weight is the load you lifted, and reps is the number of repetitions you completed with good form before you could not have done another. The formula only holds up to around 10 reps; beyond that, fatigue and muscular endurance distort the result badly enough that it should not be trusted.

Worked examples at every rep range

Using 100kg as the base weight lifted:

• 100kg × 3 reps: 100 × 36/34 = 105.9kg
• 100kg × 5 reps: 100 × 36/32 = 112.5kg
• 100kg × 8 reps: 100 × 36/29 = 124.1kg
• 100kg × 10 reps: 100 × 36/27 = 133.3kg

Notice how the estimate grows less reliable as reps increase — the formula extrapolates further and further beyond what you actually lifted, which is exactly why low-rep testing (3–6 reps) gives the most trustworthy prediction.

How accurate is the prediction, really?

Research comparing predicted 1RM formulas against directly tested maxes generally finds errors in the range of 5–10% for sets of 3–6 reps, widening to 10–15% or more once rep counts climb into double digits. A few factors move the error in either direction:

• Rep range used:the closer your test set is to a true 1–3 rep effort, the smaller the gap between predicted and actual.
• Exercise pattern: the formula is more accurate for compound barbell lifts (squat, bench, deadlift) than for exercises where technique breaks down under fatigue, such as pull-ups or overhead pressing.
• Training experience: well-trained lifters with efficient technique tend to see predictions track closer to their tested max than beginners, whose form often degrades before true muscular failure.
• How close to failure the set was taken: stopping a rep or two short of failure (a common instruction for safety) will understate the true max, since the formula assumes the set was taken to genuine technical failure.

Brzycki vs testing your actual 1RM

A calculated 1RM is an estimate, not a guarantee. It is genuinely useful for programming training percentages week to week without the fatigue and injury risk of maxing out regularly. But if you need a precise number — ahead of a powerlifting meet, for example — there is no substitute for a properly warmed-up, coached, single-rep test.

Our 1RM calculator runs the Brzycki formula automatically alongside the Epley formula, so you can compare both estimates from the same set. For a side-by-side breakdown of how the two formulas differ, see our Epley vs Brzycki comparison guide. Once you have an estimated max, our training percentages guide shows you how to turn that number into a working programme.

The bottom line

Test in the 3–6 rep range if you want the Brzycki formula to give you its most reliable number. Treat anything predicted from 10+ reps as a rough guide only. And if a number really matters — a competition total, a training max for a new block — test it directly rather than relying on any formula alone.