One-rep max calculator: estimate your 1RM from a set

How to use the calculator

1. Choose unitsPick metric or US units. Switching carries your number across, rounded to the nearest 2.5 kg or 5 lb.
2. Enter the weight and repsUse a recent set you took close to failure with clean form. The calculator takes 1 to 12 reps.
3. Read the estimateThe headline is the Epley estimate, rounded to the nearest 0.5. Brzycki sits under it as a second opinion.
4. Use the training loadsThe table turns the estimate into loads from 65% to 100% of your max, rounded to 2.5 kg or 5 lb, with the reps most people can do at each.

Your one-rep max (1RM) is the heaviest weight you can lift once with good form. Most strength programs set loads as a percentage of it. Testing it directly is tiring, takes practice and carries more risk than a normal set. Estimating it from a set of a few reps gets you close without the max attempt.

The formulas

• Epley (1985): 1RM = weight × (1 + reps ÷ 30)
• Brzycki (1993): 1RM = weight × 36 ÷ (37 − reps)

For a single rep, both return the weight you lifted. The headline number is Epley. Below 10 reps Epley gives the higher estimate, at exactly 10 the two agree, and past 10 Brzycki climbs faster. The calculator accepts 1–12 reps and rounds to the nearest 0.5 kg or lb.

A worked example

Say you squat 80 kg for 5 reps, the calculator’s default. Epley: 80 × (1 + 5 ÷ 30) = 80 × 1.167 = 93.3 kg, shown as 93.5 kg. Brzycki: 80 × 36 ÷ (37 − 5) = 80 × 1.125 = 90 kg. A gap of a few kilograms is normal; plan from the lower number if you want to be conservative. In US units the default is 175 lb for 5, which gives 204 lb by Epley and 197 lb by Brzycki.

The training-load table works from the Epley figure. At 80% it gives 75 kg, about 8 reps. At 75% it gives 70 kg, about 10. The 87% row lands back on 80 kg for 5, the set you entered, which is a good sign the numbers hang together.

This is the NSCA’s reference table, and it describes an average lifter. Some people get more reps at a given percentage, some fewer. It also varies by exercise: most people manage more reps at the same percentage on a leg press than on a bench press.

How accurate is it?

Under about 10 reps, the formulas tend to land close to a tested max. Past 10, accuracy drops. A long set tests muscular endurance and how well you tolerate fatigue as much as strength, and both vary from person to person. That is why the calculator stops at 12 and why its own note says fewer reps give a better estimate.

Two more things bend the number. The set has to be close to failure; stop with three reps in the tank and the formula sees a weaker lifter. And a true max is a skill. Lifters who rarely train heavy singles often can’t lift the full estimate on the day. Rating each set with RPE helps you judge how close to failure you were.

Safety: don’t test a true max alone

• Use safeties: Squat inside a rack with the safety pins or straps set just below your bottom position, and bench with spotter arms or a spotter.
• Warm up in steps: Work up through a few lighter singles before anything near your max.
• Stop at technique failure: If the bar path or your position breaks down, the set is over.
• Skip it when you’re new: Beginners get more from a few months of steady progressive overload than from max testing.

What to do with your 1RM

Use the estimate to set working weights. A program that calls for 3 sets of 5 at 80% means 75 kg for the lifter above. The table says most people can do 8 reps there, so each set leaves a few in reserve. That is how percentage programs build strength without grinding every set.

Then let your logs move the number. Re-estimate from your best recent set every few weeks instead of re-testing. That needs a record of sets, reps and weights. A workout tracker keeps it for you. In FORM, the live workout screen logs every set, charts your best set per lift, and suggests a heavier load after three sessions at the same weight.

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