The 1RM formula problem: Epley, Brzycki, Lombardi, and why every estimate lies

Every strength coach, every training app, every spreadsheet — they all ask you to estimate your one-rep max using some formula. And every single one of them acts like the answer is authoritative. It's not.

One-rep max estimates are useful approximations. But they're approximations built on assumptions about how strength decays as fatigue accumulates — assumptions that break down the moment your set gets hard. This article breaks down the three most commonly used formulas, shows you exactly how they diverge, and tells you which to use in which situation.

What these formulas actually are

All three are velocity-based fatigue models. They assume that the relationship between the weight you lift and the number of reps you can do at that weight follows a predictable pattern. As you approach failure, your velocity drops, and the formula converts "how fast you can move this weight" into "how much could you move for one rep."

The problem is that this relationship varies wildly between individuals. Muscle fiber composition, training history, neural efficiency, and even the exercise itself all shift the curve.

The 225 × 5 worked example

Let's run the numbers for a lifter who benches 225 for 5 reps. Here's what each formula says:

That's a 11 lb spread across three "correct" formulas. In the real world, the actual 1RM could be anywhere in that range — or outside it.

When Epley overshoots

Epley is the most popular formula and the most optimistic. It tends to overestimate the true 1RM, especially as reps increase. Why? Epley's formula was originally derived from powerlifting data where most test sets fall between 1–5 reps. It works fine in that range, but if you're using it for a 10-rep set, the estimate gets sloppy fast.

The overestimation is most pronounced for beginners, whose strength decay curves are steeper. A beginner who benches 185 × 10 gets an Epley estimate of 282 lb — a number that is almost certainly wrong. Their actual 1RM might be 230 lb.

When Brzycki plays it safe

Brzycki was developed by Matt Brzycki, a strength and conditioning specialist, specifically to address Epley's overestimation problem. It applies a slightly steeper fatigue curve, which produces more conservative estimates.

For a trained lifter with a 3-rep estimate, Brzycki is arguably the most accurate formula against actual 1RM testing data. The tradeoff: it can be too conservative at high rep ranges (10+), potentially underestimating by 10–15 lb.

Lombardi and the power curve

Lombardi uses a power-law approach — it models the fatigue curve as a gentler slope, which makes it more forgiving at moderate rep ranges (5–8). It's less commonly used but actually performs well for the exact range most recreational lifters train in.

The downside: Lombardi was developed on Olympic lifters. For raw powerlifting movements, it can be as optimistic as Epley.

The AMRAP reality check

None of these formulas account for what actually happens in a real max-effort attempt. When you attempt a true 1RM:

• Your nervous system has to recruit every motor unit simultaneously
• Technique breaks down under heavy loads, costing you output the formula doesn't measure
• Mental focus and pre-exhaustion from a warm-up set create massive variance
• Muscle fiber recruitment patterns shift at the threshold of true max effort

Studies comparing predicted 1RM against actual tested 1RM consistently find errors of ±5–12% depending on the formula and the lifter. That's a 25–60 lb swing on a 500 lb deadlift.

Which formula to use when

How to use 1RM estimates in your training

The practical reason you'd ever estimate a 1RM is to calculate working weights for percentage-based programming. If your real 1RM is 300 lb and you need to work at 80%, that's 240 lb. The formula's job is to give you that 300 lb number without having to actually test it.

Here is the key rule: if you're using percentage-based programming, always use the formula on your actual tested 1RM, not an estimated one. Predicted 1RM values compound errors when you build a program around them.

If you haven't tested a true 1RM, use the formula on your heaviest recent set and then apply a correction factor: subtract 5% for Epley, 3% for Lombardi, 0% for Brzycki.

The bottom line

None of these formulas are "correct." They're useful approximations with known error margins. Use Brzycki as your default — it's the most conservative and the most accurate across the widest rep range. Use Epley only for heavy sets (1–3 reps) from trained lifters. And always treat the result as a starting point, not a target.

If you're building a program around 1RM percentages, test a true single every 8–12 weeks. The estimate is only good if you calibrate it against reality.