Why does accuracy drop above 10 reps?

Both formulas assume the limiting factor is strength — above roughly 10 reps, muscular endurance and fatigue resistance start to matter more than raw strength, which these formulas don't account for.

Should I actually test my 1RM instead of estimating it?

A real 1RM test is more precise but carries real injury risk without a proper warm-up and a spotter — for most training and programming purposes, an estimate from a lower-rep, sub-maximal set is both safer and accurate enough.

What are the training percentages used for?

Strength coaches commonly prescribe working weights as a percentage of 1RM — for example, heavy near-maximal singles at 90-95%, primary strength work at 80-85%, and lighter volume or accessory work at 65-75% — letting you plan an entire training block from one estimated number.

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Health & Fitness

One-Rep Max Calculator

Estimate your 1RM from any weight and rep count.

🔒 Runs entirely in your browser — nothing here is ever uploaded

Last reviewed 2026-08-25

About the One-Rep Max Calculator

Estimates your one-rep max (1RM) — the heaviest weight you could lift for a single rep — from any weight and rep count you can actually complete, using the Epley and Brzycki formulas, plus a training-percentage table for programming your next workout.

How to use it

Enter the Weight you lifted and the Reps you completed with good form.
Read your estimated 1RM from both the Epley and Brzycki formulas.
Use the training-percentage table to plan working weights for a given percentage of your max.

Formula

Epley: 1RM = weight × (1 + reps ÷ 30)
Brzycki: 1RM = weight × 36 ÷ (37 − reps)

Both are long-standing strength-training formulas estimating a one-rep max from a lower-rep, sub-maximal set. Both are most accurate in roughly the 1-10 rep range this tool is built for — accuracy drops for both formulas at higher rep counts, since muscular endurance increasingly outweighs pure strength the more reps you do.

Worked example

Lifting 100 kg for 5 reps gives an Epley estimate of about 117 kg and a Brzycki estimate of about 113 kg — the two formulas typically land within a few kg of each other in this rep range, with Epley reading slightly higher as reps increase.

Interpreting your result

These are estimates, not guarantees — actual 1RM depends on technique, fatigue, and day-to-day variation. Use the estimate to guide programming, not as a number to test against without a proper warm-up and a spotter.

Recommendations

• Retest periodically (every 4-8 weeks) rather than assuming a single old estimate still reflects your current strength.
• Use the training-percentage table to plan working sets — heavy singles around 90-95%, primary strength work around 80-85%, and volume/accessory work around 65-75% of your estimated 1RM are common coaching guidelines.
• A true 1RM test carries real injury risk without a spotter and proper warm-up — for most training purposes, an estimate from a lower-rep set is both safer and sufficiently accurate.

Frequently asked questions

Neither is universally more accurate — they're both empirical estimates that tend to agree closely in the 1-10 rep range, with Epley reading a bit higher as rep count increases. Most lifters use Epley as the more commonly cited default and treat Brzycki as a cross-check.