Which 1RM formula is most accurate?

None is exact — all are regression estimates from lifters tested to failure. Epley and Brzycki are the two most cited and agree closely under about 8 reps; Lombardi's pure exponential curve tends to diverge more at higher rep counts. Use whichever the rest of your program already references.

How many reps gives the most reliable estimate?

1–5 reps. Every formula's error grows as reps increase because fatigue stops being purely mechanical — above about 10 reps, treat the number as a rough guide, not a precise prediction.

Can I use this for any lift?

Yes — the formulas are generic to any barbell, dumbbell or machine lift. They don't account for lift-specific technique factors (e.g. leg drive on bench), so treat the estimate as a training guide, not a competition prediction.

What is the percentage chart for?

It converts your estimated 1RM into common training percentages (60–100%) so you can plan work sets without recalculating by hand — e.g. 80% is a typical top-set intensity for a strength block.

One-Rep Max Calculator

Estimate your one-rep max from any weight and rep count, with Epley, Brzycki or Lombardi formulas toggled in one tool, plus a working-set percentage chart.

Loading tool…

Formula: Epley: 1RM = weight × (1 + reps/30); Brzycki: weight × 36/(37 − reps); Lombardi: weight × reps^0.10

Worked examples

100 (kg or lb) for 5 reps, Epley formula
A classic 5-rep working set; Epley is the most commonly used estimator and works the same whether the weight is kg or lb.
Same 100 for 5 reps, Brzycki formula
Brzycki tends to run lower than Epley at higher rep counts, which is why formula choice matters most past 5–6 reps.
60 for 10 reps, Lombardi formula
A higher-rep set where Lombardi's pure exponential curve gives a noticeably different estimate than Epley or Brzycki.

What a one-rep max estimate is

Your one-rep max (1RM) is the heaviest weight you could lift for a single, full-effort repetition with good form. Testing it directly is fatiguing and carries injury risk, so lifters instead do a lighter set to a few reps and estimate 1RM from a formula — which is exactly what this tool automates from any weight and rep count you enter.

The three formulas

Epley (1RM = weight × (1 + reps/30)) is the most widely cited estimator and the default here.
Brzycki (1RM = weight × 36/(37 − reps)) tends to track closely with Epley under about 6 reps but diverges more as reps climb.
Lombardi (1RM = weight × reps^0.10) uses a pure exponential curve rather than a linear one, which behaves differently at higher rep counts.

All three are toggled in this one tool rather than split across separate pages, because they take the same inputs and answer the same question — a formula choice, not a different calculator. The number you enter for weight can be kg or lb: because every formula here is a simple multiple of the weight you enter, the result comes out in whatever unit you put in, with no conversion needed.

Why the formulas disagree

Each was derived from a different dataset of lifters tested to failure at various rep counts, so they encode slightly different assumptions about how fast strength drops off as reps increase. At low reps (1–3) they agree closely; by 10–12 reps the gap between formulas can be several percent of your estimated max. None of them is "correct" in an absolute sense — they're all regression estimates, and the true relationship between reps and load varies by exercise, training history and even how close to failure the set really was.

Using the percentage chart

The table converts your estimated 1RM into common training percentages from 60% to 100%, which is how most strength programs are actually written (e.g. "3 sets of 5 at 80%"). Use it to plan work sets without recalculating fractions by hand each session. Because it's derived from an estimate, treat the chart as a planning tool — retest or recalculate periodically as your strength changes rather than anchoring to one old number indefinitely.

Limits

Estimates are least reliable above about 10 reps, where fatigue stops being purely mechanical and technique breakdown starts affecting the numbers more than any formula can capture. They also don't account for exercise-specific factors — a bench press 1RM estimate behaves differently from a squat or deadlift one because bar path, leverage and fatigue patterns differ. Use this as a training guide, not a competition-day prediction, and always warm up properly and use a spotter or safety pins when testing a true max.

Frequently asked questions

Which 1RM formula is most accurate?: None is exact — all are regression estimates from lifters tested to failure. Epley and Brzycki are the two most cited and agree closely under about 8 reps; Lombardi's pure exponential curve tends to diverge more at higher rep counts. Use whichever the rest of your program already references.
How many reps gives the most reliable estimate?: 1–5 reps. Every formula's error grows as reps increase because fatigue stops being purely mechanical — above about 10 reps, treat the number as a rough guide, not a precise prediction.
Can I use this for any lift?: Yes — the formulas are generic to any barbell, dumbbell or machine lift. They don't account for lift-specific technique factors (e.g. leg drive on bench), so treat the estimate as a training guide, not a competition prediction.
What is the percentage chart for?: It converts your estimated 1RM into common training percentages (60–100%) so you can plan work sets without recalculating by hand — e.g. 80% is a typical top-set intensity for a strength block.

These calculators give general estimates from published formulas. They are not medical advice and do not account for your individual health; talk to a qualified professional before changing your diet or training.