How to Calculate Your 1RM (One-Rep Max) Without the Guesswork

You can test your one-rep max in the gym or work it out from a hard set. Here's how to do both safely, how the formulas work and how to turn the result into training weights.

Knowing how to calculate 1RM, your one-rep max, takes a lot of the guesswork out of picking your weights. You can test a true max in the gym or estimate it from a hard set of several reps. Here's how to do both, the math behind the two most popular formulas and how to turn the number into training loads.

What is a 1RM?

Your 1RM is the heaviest weight you can lift for one clean rep in a given exercise. It's specific to the lift: your squat max tells you nothing about your bench press, so every exercise gets its own number.

It also moves around with sleep, stress and fatigue, so treat it as a snapshot.

Why bother knowing your max?

You don't need a 1RM to get stronger, but it's a genuinely useful tool:

• Setting loads. Plenty of programs prescribe weights as a percentage of 1RM, such as 5 sets of 5 at 80%. Without a max, you're guessing.
• Tracking progress. An estimated max lets you compare a set of 8 in March with a set of 4 in June on the same scale.
• Planning ahead. When you know where you stand, it's easier to map out small weekly jumps instead of overreaching or sandbagging.

That last point is really about progressive overload, gradually asking more of your body so it keeps adapting. Our guide to progressive overload covers how to build that into your plan.

How to test a true 1RM safely

A real max test gives the most accurate answer, but it's also the most demanding. Do it fresh, at the start of a session, with every attempt planned before you touch the bar.

Use a warm-up ladder

The goal is to get warm and grooved for heavy weight without tiring yourself out, so reps drop as the load climbs. Say you expect your squat max to be around 120 kg (265 lb):

1. Empty bar (20 kg), 8–10 reps
2. 60 kg (about 50%), 5 reps
3. 85 kg (about 70%), 3 reps
4. 95 kg (about 80%), 2 reps
5. 107.5 kg (about 90%), 1 rep
6. First attempt: 115 kg (about 95%)
7. Second attempt: 120 kg
8. Third attempt, only if the second one moved well: 122.5–125 kg

Rest 2–3 minutes between the lighter steps and 3–5 minutes between heavy singles. Stop as soon as your form starts to break down, even if you feel you had more left. A rep with a rounded back or caving knees doesn't count.

Get a spotter or set the safeties

On the bench press, always have a spotter standing at the middle of the bar, ready to take it if you stall. Agree beforehand on when they should step in, so nobody grabs the bar too early or too late. For squats, test inside a power rack with the safety bars set just below your bottom position, or use one or two experienced spotters.

The deadlift doesn't need a spotter in the same way, since you can simply put the bar down. The real risk there is letting your back position slip as the weight gets heavy.

When not to test

• You've been lifting for less than a few months and your technique isn't consistent yet. Estimate instead.
• You're in pain, ill or coming back from an injury.
• You slept badly or you're still beat up from a hard session the day before.
• You have no spotter or safeties for the lifts that need them.
• You have a condition such as high blood pressure or a heart problem. Talk to your doctor before attempting maximal lifts.

How to calculate 1RM from a multi-rep set

For most lifters, estimating is the smarter route. Take a hard set of 3–10 reps, close to failure, and plug it into a formula. The load is lower, the risk is lower and you can do it in a normal session. The two most widely used formulas come from Epley and Brzycki.

The Epley formula

1RM = weight × (1 + reps / 30)

Example: you bench 100 kg (220 lb) for 5 reps. 5 divided by 30 is about 0.167, so 100 × 1.167 gives roughly 116.7 kg (about 257 lb).

The Brzycki formula

1RM = weight × 36 / (37 − reps)

Same set: 100 × 36 / (37 − 5) = 3,600 / 32 = 112.5 kg (about 248 lb).

So the two formulas don't agree perfectly; here they're a little over 4 kg apart. Another example: 80 kg (176 lb) for 8 reps gives 101.3 kg with Epley and 99.3 kg with Brzycki. At exactly 10 reps they give the same result, and below 10 reps Brzycki comes out slightly lower than Epley.

Which one you pick matters less than using the same one every time.

Getting a reliable estimate

• Use a set that genuinely ended close to failure, with no more than one or two reps left.
• For the most dependable number, choose a set of 3–6 reps.
• Count only reps with solid form and your normal range of motion.
• Use your first work set, not the last one when you're already fatigued.

1RM percentage chart

The table below gives approximate guidelines for what share of your 1RM you can typically lift for a given number of reps. These aren't exact figures; they vary from person to person and from lift to lift.

Why estimates get shakier above about 10 reps

The more reps you do, the more the set tests muscular endurance rather than max strength. Two people with the same 1RM can get very different numbers of reps at 70%, depending on muscle fiber makeup, training history and the kind of work they're used to.

You can see it in the formulas as well. 60 kg (132 lb) for 15 reps gives 90 kg with Epley but 98.2 kg with Brzycki, a gap of more than 8 kg. Brzycki's formula also breaks down completely as the rep count approaches 37.

Stick to sets of roughly 3–10 reps when you calculate 1RM. If all you have is a set of 12–15, treat the result as a rough ballpark.

Using percentages of your 1RM in training

Once you have a 1RM, tested or estimated, you can work out your program weights. Say your squat max is 120 kg (265 lb):

• 70% = 84 kg, good for sets of 8–10
• 75% = 90 kg, good for sets of 6–8
• 80% = 96 kg, good for sets of 4–6
• 85% = 102 kg, good for sets of 3–5

Round to the plates you have, for example 85 or 82.5 kg instead of 84. Notice that these rep ranges leave a couple of reps in reserve. A program stays sustainable when most sets stop a little short of failure.

Work from a training max

Many experienced lifters don't program off their true 1RM but off a training max, often around 90% of it. With a 120 kg max, the training max is 108 kg, and 80% of that is about 86 kg. That builds in a buffer for bad days and lets you add weight steadily for weeks before you stall.

Update the number regularly

Your 1RM has a shelf life. Recalculate it every few weeks, for example from your heaviest set of the week. In TANK you log every set with weight and reps, so the data for a fresh estimate is already there when you need it. If a heavy set felt off, you can also film it and let the AI technique analysis score it from 0 to 100 with rep-by-rep feedback.