One-rep max calculator

How it works

It uses the Epley formula: one-rep max = weight × (1 + reps ÷ 30). It is most accurate for sets of about 2 to 10 reps taken close to failure. Sets above 12 reps say too little about your maximum, so they aren't used.

Using your one-rep max

Most strength programmes give weights as a percentage of your one-rep max. For building muscle, 65 to 80 percent for 6 to 12 reps works well. For strength, 80 to 90 percent for 3 to 6 reps. You don't need to test a true single to train this way: a recent hard set is enough.

An estimate is not a target. Tiredness, sleep and technique all change what you can lift on the day.

Questions

Is it safe to test my one-rep max?

For most people an estimate from a set of 3 to 8 reps is safer and accurate enough. If you do test a true single, warm up well, use a spotter or safety bars, and stop if your form breaks down.

How accurate is a 1RM calculator?

Usually within a few percent for sets of 2 to 10 reps. It is less accurate for very long sets and for lifts you have little practice with.

Which lifts can I use it for?

Any lift you can load steadily, such as squats, bench press, deadlifts, presses and rows. It suits isolation exercises less well.

The same calculators are built into the RepSensei workout log, next to your sets.

• Barbell plate calculator
• Warm-up sets calculator