Testing an actual one-rep max, the heaviest weight you can lift for a single rep, is fatiguing, carries real injury risk without supervision, and usually isn’t necessary. Strength coaches have relied on regression formulas for decades to estimate 1RM from a lighter, safer, multi-rep set instead — and two formulas in particular have stood the test of time.
The Two Formulas
The Epley formula, developed by strength coach Boyd Epley in the 1980s, is: 1RM = weight × (1 + reps ÷ 30). It assumes a roughly linear relationship between reps performed and percentage of your true max.
The Brzycki formula, created by Matt Brzycki in 1993, is: 1RM = weight ÷ (1.0278 − 0.0278 × reps). It uses a curve that gets steeper as reps climb toward its theoretical maximum of 37 reps.
In practice, the Brzycki formula tends to be favored for lower rep ranges (2-6 reps), while Epley is often considered more accurate at higher rep ranges (7-10+). Both formulas are most reliable between 3 and 8 reps; past about 10 reps, muscular endurance starts to influence the set more than raw strength, and the estimate becomes less trustworthy.
Calculate Your Estimated 1RM
Enter the weight and reps from a recent set (ideally 3-8 reps, taken close to failure).
Why This Number Is Useful
- Programming training percentages (e.g., “work at 75% of 1RM for 8 reps”) without needing to actually max out
- Tracking strength progress over months without the fatigue cost of frequent max-effort testing
- Setting realistic, individualized starting loads for a new program
The Limitations Worth Knowing
A calculated 1RM is generally accurate within about 3-5% for most lifters, but it can’t account for your central nervous system readiness, motivation, or technique breakdown at true maximal loads on a given day. It also tends to be somewhat less accurate for less experienced lifters, whose technique may change meaningfully under heavier loads in ways a formula can’t predict. Treat the number as a solid programming estimate, not a guaranteed number you’d hit if you tried it for real.
Frequently Asked Questions
Which formula is more accurate, Epley or Brzycki? Neither is universally “more accurate” — Brzycki tends to run slightly lower and suits lower rep sets better, while Epley runs slightly higher and suits higher rep sets better. Many lifters compare both and take the number in between as a reasonable estimate.
Should beginners test their actual 1RM? Generally not recommended without a knowledgeable coach and good technique first — the injury risk from maximal loads with imperfect form outweighs the benefit for most beginners, and a calculated estimate serves the same programming purpose more safely.
How often should I recalculate my 1RM? Every 4-8 weeks is common for people following a structured strength program, using whatever heaviest set (in the 3-8 rep range) you happened to complete recently rather than a dedicated max-effort test.
Why Estimate Instead of Testing Directly
Your one-rep max, the maximum weight you can lift for a single repetition with proper form, is a useful benchmark for programming training intensity, but testing it directly carries real risks: maximal attempts require a full nervous system and muscular effort at the technical limits of your strength, which meaningfully increases injury risk, especially for lifters without extensive experience or a spotter, and it demands significant fatigue and recovery time around the test itself. Formulas like Epley and Brzycki estimate your one-rep max from a lighter, safer set, typically performing 3-10 reps at a challenging but manageable weight, then applying a mathematical relationship between reps performed and percentage of true one-rep max to calculate an estimate without needing to actually attempt the maximal lift.
This approach reflects a well-established relationship in strength training: as weight decreases from your true one-rep max, the number of reps you can perform at that lighter weight increases in a fairly predictable pattern, which is the mathematical basis both formulas rely on, using slightly different equations that produce similar but not identical estimates.
How Accurate These Formulas Actually Are
Research validating these formulas against actual measured one-rep max values generally finds reasonable accuracy for estimates based on lower rep counts (3-6 reps), with accuracy declining as the rep count used for estimation increases, estimates based on sets of 10 or more reps tend to be noticeably less reliable than estimates from sets of 3-5 reps, since the relationship between reps and load becomes less linear and more individually variable at higher rep ranges. Accuracy also varies somewhat by exercise, compound, multi-joint lifts and isolation exercises don’t always follow identical rep-to-load relationships, and by training experience, since technique consistency and fatigue tolerance affect how closely someone’s real performance matches the formula’s underlying assumptions.
Given this, these calculators are best treated as a reasonably reliable estimate for programming purposes, useful for calculating training percentages for a periodized program, rather than a precise substitute for an actual tested max when true precision matters, like for a powerlifting competition.
Using the Estimate Safely and Effectively
For most strength training purposes, calculating your one-rep max from a submaximal set, then using percentages of that estimate to structure training phases (lower percentages for higher-rep volume phases, higher percentages for strength-focused phases), is both safer and more practical than regularly testing a true max. If you do want to test an actual one-rep max, doing so with a qualified spotter, a proper warm-up progression building up to the attempt, and adequate recovery beforehand meaningfully reduces the risk involved, and this is generally reserved for experienced lifters with solid technique rather than beginners still building foundational strength and movement competency.
Sources
Final Thoughts
You don’t need to grind out a genuine max-effort lift to know roughly where your strength stands. A recent working set of 3-8 reps, run through the Epley or Brzycki formula, gets you close enough for programming purposes with none of the fatigue or injury risk of an actual 1RM attempt.
About the Author
This article was written and reviewed by Ethan Brooks, focused on translating public health information into clear, practical guidance for everyday readers. If you spot an error or have a correction, please contact us.