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One-rep max calculator

Estimate your 1RM from a set taken to failure with the Epley formula. Free calculator with a 50–95% training-load table for programming.

Your one-rep max is the heaviest weight you can lift for one full rep with good form. Many strength programs, 5/3/1 and Sheiko among them, set working weights as a percentage of it, so you need a number. You can estimate it from a hard set instead of testing it under a maximal load.

Enter the weight and the reps you completed on a set taken to failure or close to it. You get an estimated 1RM and a table of working weights at common percentages. MuscleBuddy uses the same formula when it estimates your max from the sets you log.

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

For two or more reps, the Epley formula is 1RM = weight × (1 + reps / 30). For a single, the estimate is the weight itself: the formula would put a 100 kg single at 103.3 kg, which is a max you haven't shown, so the calculator returns 100 kg. Each extra rep adds about 3.3% of the bar weight to the estimate.

A 100 kg × 5 set gives 100 × (1 + 5/30) = 116.7 kg. A 100 kg × 3 set gives 110 kg. Epley is most reliable up to about 10 reps. Beyond that, endurance plays a bigger part in how many reps you get, so treat a high-rep estimate as rough. The calculator takes sets of up to 20 reps.

The formula assumes the set went to failure. A set you ended with reps left over gives a lower estimate than your real max. If you know how many you had left, add them to the rep count: 100 kg × 5 with two in reserve goes in as 7 reps.

The table below turns your estimate into working weights. Roughly, 90–95% suits singles and doubles, 80–85% triples and sets of four, 70–80% sets of 5 to 8, and 60–70% higher-rep accessory work. Results are rounded to 2.5 kg or 5 lb so you can load them with standard plates.

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?
On sets of 10 reps or fewer taken to failure, Epley usually lands within about 5% of a tested max. Past 10 reps it gets less reliable, because muscular endurance starts to decide the rep count more than strength does. This calculator takes sets of up to 20 reps.
How many reps should I use for the most accurate estimate?
A set of 3 to 5 reps taken to failure, or to within a rep of it, gives the most reliable estimate. If you stopped with reps left, add them to the count: 5 reps with 2 in reserve goes in as 7. A single needs no formula, since the weight you lifted is your max for that day.
Should I test my actual 1RM or use a calculator?
For programming, an estimate is enough. A true max test is fatiguing and carries more risk, and it earns its place at the end of a peaking block or at a meet, where the number itself is the goal.
Can I use this for any lift?
It works best on compound barbell lifts: squat, bench, deadlift, overhead press, row. Rep-to-strength relationships differ between exercises, so treat estimates for machines and isolation work (curls, lateral raises) as rough.
How often should I update my 1RM?
Every 4–8 weeks, or whenever you set a new best top set. If your strength is climbing, percentages based on an old max will feel lighter each week.

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