1RM Calculator

Your one rep max, or 1RM, is the heaviest weight you can lift for a single repetition with good form. It's a common way to measure strength and to plan training, because many programmes are written as percentages of your 1RM.

Testing a true 1RM can be risky, especially without experience or a spotter. Fortunately, you can estimate it from a heavier set of several reps. To do that, use the one rep max calculator.

What is a one rep max?

A 1RM is specific to each exercise. Your 1RM for the squat will be different from your bench press or deadlift. It also changes as you get stronger, so it's worth re-estimating every few weeks or months if you're following a programme.

Why estimate rather than test?

Lifting your absolute maximum puts a lot of stress on muscles, joints and connective tissue, and the risk of injury is higher, particularly if your technique breaks down. Estimating from a set of, say, 3 to 8 reps gives a good approximation with less risk and less fatigue.

How the formulas work

Several formulas convert a weight and number of reps into an estimated 1RM. The most widely used are:

Each formula gives a slightly different result, so the calculator shows all three and averages them.

A worked example

You squat 80kg for 5 good reps:

• Epley: 80 × (1 + 5 ÷ 30) = about 93.3kg (shown rounded to 93.5kg)
• Brzycki: 80 × 36 ÷ 32 = 90kg
• Lombardi: 80 × 5 to the power of 0.1 = about 94kg
• Average estimate: about 92.5kg

How accurate are the estimates?

The formulas are most accurate when you use sets of 2 to 10 reps. Above about 10 to 12 reps, estimates become less reliable, because endurance plays a bigger part. Results also vary between people and exercises: some people can do more reps at a given percentage than others.

For the best estimate, use a set taken close to failure with good form, and use the same exercise technique each time.

Using percentages of your 1RM

Once you know your estimated 1RM, you can use it to choose training weights. As a rough guide:

These ranges are approximate. The calculator gives a full table of weights for your estimate.

Safety tips

• Warm up properly, with lighter sets building up to your working weight.
• Use a spotter or safety bars for exercises like the bench press and squat.
• Prioritise good technique over adding weight.
• Stop if you feel pain, rather than discomfort from effort.
• Allow rest between heavy sessions so your body can recover.

Strength training and health

The UK Chief Medical Officers recommend that adults do activities that build strength on at least two days a week, alongside at least 150 minutes of moderate activity. Strength training helps maintain muscle, bone density and balance, which become increasingly important with age. You don't need heavy weights to benefit: body-weight exercises and resistance bands count too.

Tracking progress

Your estimated 1RM is a useful way to track progress over time. If your estimate rises from 92.5kg to 100kg over a few months, you've become measurably stronger, even without testing a true maximum.

Progressive overload: getting stronger over time

Strength improves when you gradually ask your muscles to do a little more than they're used to. This principle, called progressive overload, can be applied in several ways: adding a small amount of weight, doing an extra rep or set, slowing the lowering phase, or reducing rest between sets. Small, regular increases are more sustainable than big jumps. For example, adding 2.5kg to a lift each week or two, while keeping good technique, can lead to steady progress for many months, particularly for newer lifters.

Recovery matters just as much as training. Sleep, enough protein and rest days allow your body to adapt. If your estimated 1RM stops improving for several weeks, it can be a sign to change your programme, take a lighter week or look at sleep and nutrition. Keeping a simple log of the weights and reps you complete makes it easy to see trends and to calculate an up-to-date estimate whenever you need one.

Choosing which set to use

For the most useful estimate, use your heaviest working set of the day, completed with good form and taken close to failure. A set where you clearly had several reps left will underestimate your 1RM, while a set where your technique broke down may overestimate what you can safely lift.