One Rep Max Calculator

Estimate your one-rep maximum using six validated formulas and get a full training zone percentage table.

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Weight Lifted (kg)

Reps Performed (1 – 20)

Most accurate between 1–10 reps. Higher rep counts reduce precision.

Tip: For the most accurate estimate, test with 3–6 reps at a challenging but controlled weight.

Average 1RM (6 formulas)

–

Enter weight lifted and reps

Epley (Best Estimate)

–

W × (1 + R/30)

Brzycki

–

W × 36/(37 − R)

Lombardi

–

W × R^0.1

Mayhew

–

(100W) / (52.2 + 41.9e^(−0.055R))

% of 1RM	Weight	Training Zone	Purpose
Calculate to see training zones

Estimate your one-repetition maximum (1RM) for any lift from a submaximal set, using six validated strength formulas, plus a full training percentage breakdown.

How It Works

How One Rep Max Calculator Works

Each formula estimates how much weight you could lift for a single rep based on the weight and reps you actually performed. Epley's formula — W × (1 + reps ÷ 30) — is one of the most commonly cited; Brzycki's — W × 36 ÷ (37 − reps) — tends to run slightly more conservative at higher rep counts; and Lombardi, Mayhew, O'Conner, and Wathan each use their own exponential or fractional adjustment derived from different research samples.

Because all six formulas are estimates built on different underlying assumptions, they naturally disagree with each other — sometimes by several percent — which is why the calculator averages all six into a single blended figure rather than presenting any one as definitive.

The training zone table then applies standard strength-training percentages (50% for endurance work up to 100% for a true 1RM attempt) to your estimated maximum, giving target training weights for different goals like hypertrophy (around 70%) or near-maximal strength work (90%+).

Worked Example

See It In Action

Lifting 100 kg for 5 reps produces estimates of 116.7 kg (Epley), 112.5 kg (Brzycki), 117.5 kg (Lombardi), and 119.0 kg (Mayhew) — averaging across all six formulas to roughly 115.8 kg as the estimated one-rep max. A hypertrophy-focused training zone at 70% of that would suggest working sets around 81 kg.

Real-World Use Cases

Who Uses One Rep Max Calculator and Why

Estimating your true one-rep max from a heavier submaximal set, without needing to actually attempt a maximal lift.
Setting percentage-based training weights (like 70% for hypertrophy work) from an estimated max.
Tracking estimated strength progress over time from regular training sets rather than infrequent max-out sessions.

Common Mistakes

Mistakes to Avoid

Using a set with a very high rep count (15+) to estimate 1RM — accuracy drops noticeably outside the roughly 1-10 rep range, since endurance starts to influence the result more than raw strength.
Trusting a single formula's output as exact rather than looking at the averaged blend the calculator provides — the six formulas can disagree by several percent for the same set.
Attempting to actually test a true 1RM without a proper warm-up, good form, or a spotter present, when working from the estimate would be safer for most training purposes.

Pro Tips

Tips for Best Results

Use a controlled, challenging set of 3-6 reps for the most reliable estimate — this range balances enough load to reflect real strength without excessive fatigue skewing the result.
Re-test periodically as your strength changes rather than treating one estimate as fixed for the long term.

Troubleshooting

Fixing Common Problems

My estimated 1RM feels higher than what I could actually lift. — This is common with high-rep sets, where fatigue and muscular endurance inflate the formula's estimate — try re-estimating from a lower-rep, higher-intensity set (3-6 reps) for a more realistic number.

Glossary

Terms Explained

1RM (One-Rep Max): The maximum weight you could lift for a single complete repetition with proper form.

FAQ

Frequently Asked Questions

How accurate is an estimated 1RM compared to actually testing it?

These formulas are reasonably reliable within the 1–10 rep range, but accuracy drops noticeably at higher rep counts, since fatigue and muscular endurance start to influence the result more than raw strength. For competition-level precision, an actual tested 1RM is always more reliable.

Why do the six formulas give different results?

Each was derived from a different research study, lifting population, and rep range, so small variations between them are expected and normal — averaging them, as this calculator does, tends to smooth out individual formula quirks.

What rep range gives the most accurate estimate?

Testing with 3–6 reps at a controlled, challenging weight generally produces the most reliable 1RM estimate — very high rep sets (15+) introduce more error since endurance becomes a larger factor than pure strength.

Is it safe to actually attempt a true 1RM?

Only attempt a true maximal single lift with proper form, adequate warm-up, and ideally a spotter present — for most training purposes, working from an estimated 1RM to set percentage-based training weights is both safer and just as useful.