What is a one-rep max (1RM)?

Your one-rep max is the heaviest load you can lift for a single, full-range repetition of a given exercise. It is the standard reference point used to prescribe training percentages.

How accurate is the Epley 1RM formula?

For sets in the 1–10 rep range, Epley usually lands within about 5% of a tested max. It drifts above 10 reps, because at that point how long you can hold on matters more than how much you can lift.

How many reps should I use for the most accurate estimate?

Sets of 3 to 5 reps taken to one or two reps shy of failure give the cleanest estimate. Singles only tell you exactly what you lifted; high-rep sets tend to overstate your max.

Should I test my actual 1RM or use a calculator?

An estimate is enough for almost everyone, almost all of the time. You need a number to program around, not a number to frame. A true max test carries real risk and mostly earns its place in the last weeks of a peaking block, when the number is the point.

Can I use this for any lift?

Yes. The Epley formula is exercise-agnostic: it works for squats, benches, deadlifts, presses, and rows. Isolation exercises with very short ranges of motion (curls, lateral raises) are less reliable.

How often should I update my 1RM?

Every 4–8 weeks, or after any block where you set a new top set. Training percentages drift out of date fast if your strength is climbing.

One-Rep Max Calculator

Estimate your true 1RM from any rep-max set with the Epley formula. Free strength calculator plus a full 50–95 percent training-load table for programming.

Your one-rep max is the heaviest weight you can lift for a single clean rep, and most programs worth running (5/3/1, Sheiko, RP) prescribe your working weights as a percentage of it. So you need the number. You just don't need to go find it under a loaded bar.

The Epley formula estimates it from any hard set in the 1–10 rep range. Plug in your last top set and you get a working 1RM to program around, without the risk of an actual max attempt. It's the same formula MuscleBuddy uses when it sets your percentage work.

Enter the weight you lifted and the number of clean reps you completed, ideally a set taken to one or two reps shy of failure. You'll get your estimated 1RM plus a percentage table covering the loads you'll actually train at.

Weight lifted

Reps completed

Units

Estimated 1RM117.5 kg

Training-load table

95%110 kg

90%105 kg

85%100 kg

80%92.5 kg

75%87.5 kg

70%82.5 kg

65%75 kg

60%70 kg

50%57.5 kg

How this works

The Epley formula is 1RM = weight × (1 + reps / 30). Boyd Epley popularized it in the 1980s; it sits alongside Brzycki and Lander as one of the three formulas you'll see everywhere. It assumes each additional rep costs you a roughly fixed slice of intensity, about 3.3%, as the load backs away from your true max.

For a 100 kg × 5 set, Epley estimates a 1RM of 100 × (1 + 5/30) = 116.7 kg. For a 100 kg × 3 set, the estimate drops to 110 kg, which tracks, because a heavier set for fewer reps is a more honest read on how strong you are. Above 10 reps the estimate drifts, because pacing and endurance start doing the work that force production was doing.

Use a set with one or two reps in reserve. Not a grinder, not a set you walked away from with three in the tank. A set where you barely finished the last rep will flatter you; a conservative one will sell you short.

Once you have your 1RM, the percentage table below shows the working weights for common intensity zones: 90–95% for singles and doubles (peaking), 80–85% for triples and 4s (strength), 70–80% for 5–8 rep work (hypertrophy + strength), and 60–70% for higher-rep accessory and volume work. Round to the nearest plate-compatible increment, 2.5 kg or 5 lb, so the load is actually loadable on a standard barbell.

Frequently asked questions

What is a one-rep max (1RM)?: Your one-rep max is the heaviest load you can lift for a single, full-range repetition of a given exercise. It is the standard reference point used to prescribe training percentages.
How accurate is the Epley 1RM formula?: For sets in the 1–10 rep range, Epley usually lands within about 5% of a tested max. It drifts above 10 reps, because at that point how long you can hold on matters more than how much you can lift.
How many reps should I use for the most accurate estimate?: Sets of 3 to 5 reps taken to one or two reps shy of failure give the cleanest estimate. Singles only tell you exactly what you lifted; high-rep sets tend to overstate your max.
Should I test my actual 1RM or use a calculator?: An estimate is enough for almost everyone, almost all of the time. You need a number to program around, not a number to frame. A true max test carries real risk and mostly earns its place in the last weeks of a peaking block, when the number is the point.
Can I use this for any lift?: Yes. The Epley formula is exercise-agnostic: it works for squats, benches, deadlifts, presses, and rows. Isolation exercises with very short ranges of motion (curls, lateral raises) are less reliable.
How often should I update my 1RM?: Every 4–8 weeks, or after any block where you set a new top set. Training percentages drift out of date fast if your strength is climbing.

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