How accurate is an estimated 1RM?

For sets of about 1 to 6 reps the estimate is usually within a few percent of a true max. Accuracy drops as reps climb, because fatigue, conditioning, and technique start to dominate — a 1RM predicted from a set of 15 can be off by 10% or more. Use a low-rep set (3–6) for the most reliable number, and treat the result as a starting point, not gospel.

What is the difference between the Epley and Brzycki formulas?

Both turn a weight-and-reps set into a predicted single. Epley (1RM = weight × (1 + reps ÷ 30)) tends to read slightly higher and is often favored for higher rep sets. Brzycki (1RM = weight × 36 ÷ (37 − reps)) reads a touch lower and is popular for low-rep work. They agree exactly at one rep and diverge as reps rise, which is why this calculator shows both and averages them.

Which formula should I use?

If you do not have a preference, use the average of the two — it smooths out their individual biases. If you must pick one: Brzycki is a common default for 2–6 rep sets, Epley for 7+ reps. The honest answer is that no formula is perfect; the difference between them is usually smaller than your day-to-day variation in the gym.

How do I use the percentage table to train?

Once you know your 1RM, most programs prescribe work as a percentage of it: 5 sets of 3 at 85%, say, or 3 sets of 10 at 70%. Find the percentage in the table and it tells you the load to put on the bar and roughly how many reps that load is good for. It turns an abstract program into concrete numbers for your lifts.

Why does the calculator switch to Epley for very high reps?

The Brzycki formula divides by (37 − reps), so at exactly 37 reps it divides by zero, and above 37 it produces a negative, meaningless number. To keep the result sensible, the calculator falls back to the Epley estimate whenever you enter 37 reps or more. In practice you should not estimate a 1RM from sets that long anyway — the error is enormous.

Does estimated 1RM work for any exercise?

It works best for big compound barbell lifts — bench press, squat, deadlift, overhead press — where the movement is stable and reps fail cleanly. It is less reliable for isolation moves, machines with assistance, or exercises limited by grip or balance rather than the target muscle. Calculate a separate 1RM for each lift; they do not transfer.

How often should I retest or recalculate my 1RM?

Every few weeks of consistent training is plenty. Strength changes slowly, so recalculating after every session just chases noise. A practical habit is to log a hard top set each week and re-run the estimate; when the predicted 1RM has clearly climbed, update the percentages your program uses.

Health

One Rep Max Calculator

Estimate your one-rep max from a weight and the reps you hit. See both the Epley and Brzycki estimates, their average, and the load for every training percentage. Results update live, in pounds or kilograms.

Estimate your one-rep max

Weight liftedlb

Reps performedreps

Estimated 1RM

258lb

Average of the Epley and Brzycki estimates.

Epley

263 lb

Brzycki

253 lb

Train at % of 1RM

90%232 lb3–4 reps
80%206 lb7–8 reps
70%180 lb10–12 reps
60%155 lb15–18 reps

Full table below.

Updates live

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The basics

What is a one-rep max?

Your one-rep max — 1RM — is the most weight you can move for a single clean repetition of a lift. It is the universal yardstick of strength and the number every percentage-based program is built around. Because testing a true max is tiring and risky, lifters estimate it from a set they have already done at a lighter weight for several reps.

1RM = the heaviest single

A measure of maximal strength

The most weight you can lift once. It captures peak strength in a single figure you can track over time and compare between lifts.

One clean rep, full range, good form

estimate, don’t test

Predicted from a rep set

Grinding out a true max is hard on the body. A submaximal set — a comfortable weight for a known number of reps — predicts it safely.

225 lb × 5 → ≈ 260 lb 1RM

Method

How a 1RM is estimated

Two well-known formulas turn a weight-and-reps set into a predicted single. This calculator runs both and averages them.

1
Apply the Epley formula
Multiply the weight by one plus the reps over thirty. Epley tends to read a little higher, especially as reps climb.
1RM = w × (1 + reps ÷ 30)
2
Apply the Brzycki formula
Multiply the weight by thirty-six, divided by thirty-seven minus the reps. Brzycki reads slightly lower and suits low-rep sets.
1RM = w × 36 ÷ (37 − reps)
3
Average the two
Add the two estimates and halve them. The mean evens out the small bias each formula carries on its own.
1RM ≈ (Epley + Brzycki) ÷ 2

The two formulas

Epley vs. Brzycki

They share the same job and agree exactly at one rep, then drift apart as the reps rise. Neither is “right” — which is why we show both and the average.

1RM = w × (1 + reps ÷ 30)

Epley (1985)

Linear in the reps, so it keeps climbing steadily. It is often the more generous of the two on higher-rep sets, and a common choice for sets of seven or more.

200 × (1 + 10 ÷ 30) = 267

1RM = w × 36 ÷ (37 − reps)

Brzycki

A reciprocal curve that rises faster as reps approach thirty-seven — and breaks down there, which is why it falls back to Epley at very high reps. Popular for low-rep, near-maximal work.

200 × 36 ÷ (37 − 10) = 267

Worked examples

See it across the big lifts

The same two formulas run on a bench, a squat, a deadlift, and a long high-rep set — only the numbers change.

Given Bench press: 185 lb for 5 reps

Epley: 185 × (1 + 5 ÷ 30) = 216 lb

Brzycki: 185 × 36 ÷ (37 − 5) = 208 lb

Average: (216 + 208) ÷ 2

Estimated 1RM ≈ 212 lb

Reference

The percentage-of-1RM table

Programs prescribe work as a share of your max — “3 × 5 at 85%”, “3 × 10 at 70%”. Enter your 1RM and read the load for every intensity, plus the reps each percentage is good for. This is the table you keep open between sets.

Your 1RM

The load to put on the bar for every training intensity, with the reps each is good for.

% of 1RM	Load	Reps	Good for
100%	300 lb	1	Maximal — a true single
95%	285 lb	2	Peak strength
90%	270 lb	3–4	Strength
85%	255 lb	5–6	Strength
80%	240 lb	7–8	Strength / hypertrophy
75%	225 lb	8–10	Hypertrophy
70%	210 lb	10–12	Hypertrophy
65%	195 lb	12–15	Hypertrophy / endurance
60%	180 lb	15–18	Endurance
55%	165 lb	18–20	Endurance
50%	150 lb	20+	Warm-up / technique

In practice

Using 1RM to program your training

Once you have a max for each lift, the percentage table turns any program into bar weights. The intensity you train at decides what you build.

85–100%

Strength & power

Heavy singles to triples. Builds maximal force and the skill of lifting near your limit. Long rests, low total reps, high focus.

67–85%

Hypertrophy

The classic muscle-building range — sets of six to twelve. Enough load to challenge the muscle, enough volume to grow it.

50–67%

Endurance & technique

Lighter, higher-rep work for conditioning, warm-ups, and grooving form on a new movement before the weight goes up.

Worth knowing

Accuracy and its limits

An estimate is only as good as the set it comes from. A few facts keep the number honest.

fewer reps = sharper

Low reps predict best

A set of three to six reps gives the tightest estimate. The further you push past that, the more fatigue and conditioning muddy the prediction.

high reps drift

Long sets overshoot

Estimating from fifteen-plus reps can be off by ten percent or more, because endurance, not raw strength, starts deciding when the set ends.

per-lift

Maxes don’t transfer

Your bench, squat, and deadlift maxes are unrelated. Calculate and track each separately — one cannot stand in for another.

a starting point

It’s a guide, not a guarantee

Treat the number as a sensible place to begin, then adjust by feel. Sleep, food, and stress swing a real max by several percent on any given day.

Pitfalls

Common mistakes

The errors that make an estimate useless — and how to dodge them.

count clean reps only

Counting grindy reps

Half-reps and assisted reps inflate the estimate. Only count repetitions you completed with full range and solid form.

use a real top set

Estimating from a warm-up

A weight you could have done for many more reps gives a flat prediction. Use a genuinely challenging set, close to failure.

keep the unit straight

Mixing pounds and kilos

Entering kilos while reading the table as pounds throws every load off by more than double. Set the unit once and keep it consistent.

don’t test recklessly

Maxing out cold

Chasing a true single without a proper warm-up or a spotter is how people get hurt. An estimate exists precisely so you don’t have to.

More health tools

Round out the picture

Strength sits inside the bigger health picture. Check where your bodyweight lands with the BMI calculator, and make sure you are fueling the work with the water intake calculator. Hydration and recovery move your numbers as much as any program.

FAQ

Common questions

Your one-rep max is the heaviest weight you can lift for a single, full repetition of an exercise with good form. It is the standard measure of maximal strength and the anchor for percentage-based training programs. Rather than test it directly — which is risky and tiring — this calculator estimates it from a heavier-rep set you have already done.

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