One-rep max calculator

What a one-rep max is, and why it's useful

Your one-rep max (1RM) is the heaviest weight you can lift for one clean rep of a specific exercise. It's a simple snapshot of how strong you are on that lift right now.

You don't need to actually lift your max to get value from the number. Many strength programs set weights as a percentage of 1RM, such as "3 sets of 5 at 80%," so a sensible estimate lets you follow them without guessing. It also gives you an easy way to track progress. If your estimated bench press max climbs from 80 kg to 90 kg over a few months, your training is working.

Testing a true max is tiring and riskier than normal training. Estimating it from an ordinary working set gives you most of the benefit with far less risk.

The formulas

Both formulas estimate your one-rep max (1RM) from a weight and the number of clean reps you did with it:

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

They agree closely in the 2–10 rep range, so the calculator shows their average. Both rest on the same idea: the more reps you can do with a weight, the further that weight sits below your max.

Worked example

You squat 100 kg for 5 reps:

• Epley: 100 × (1 + 5 ÷ 30) = 116.7 kg
• Brzycki: 100 × 36 ÷ 32 = 112.5 kg
• Average: about 114.5 kg

The two formulas land about 4 kg apart here. That's a useful reminder that any estimate is a range, not an exact figure. Think of 114.5 kg as "somewhere around 112 to 117 kg."

Getting a good estimate

1. Warm up properly, then do one set of 3–8 reps with a weight that's genuinely hard.
2. Count only reps with good form. Stop when the next rep would be ugly or slow to a crawl.
3. Use the estimate to plan training, and re-check every few weeks as you get stronger.

Squats and bench presses near your limit should always be done with safety bars set at the right height or with a spotter. More detail in how to estimate your one-rep max safely and progressive overload.

Why 3–8 reps works best

A set of 1 or 2 reps is already close to a true max, so it carries much of the same risk. Above about 10 reps, breathing, muscle endurance and how much discomfort you can tolerate start to matter more than raw strength, and the estimate gets less reliable. The calculator accepts up to 15 reps, but the number is most trustworthy when your set falls between 3 and 8.

Test when you're fresh

Do your test set early in a session, right after your warm-up. If you slept badly, are sore, or are getting sick, the result will come out low, so don't build a whole training block around it.

Use the same standard every time

A rep only counts if it meets your normal standard: the same squat depth, the bar touching your chest without bouncing on the bench press, a full lockout on the deadlift. Half reps inflate the estimate and make the percentages you train with too heavy.

How to use percentages to plan training

Once you have an estimate, the calculator's chart turns it into weights for common percentages of your max. As a rough guide, this is how many reps most people can manage at each level:

• 95% of 1RM: about 2 reps
• 90%: about 3–4 reps
• 85%: about 5–6 reps
• 80%: about 7–8 reps
• 75%: about 9–10 reps
• 70%: about 11–12 reps
• 65%: about 13–15 reps
• 60%: about 15–20 reps

These numbers describe a set taken close to failure. In normal training, you'll usually pick a weight that lets you finish your target reps with a rep or two to spare. Sets of 5, for example, are commonly done at around 80–85% of 1RM. That's heavy enough to build strength, but light enough to keep every rep clean.

Using the worked example above, a 114.5 kg estimate puts 80% at about 91.5 kg and 85% at about 97.5 kg. Round to the nearest weight you can actually load on the bar.

As a loose pattern, heavier sets of 1–5 reps emphasize strength, while moderate sets of 6–12 reps suit muscle building and general fitness. If you're just getting started, a structured plan such as the beginner strength training plan is easier than picking percentages on your own.

Reps in reserve: another way to choose your weights

Reps in reserve (RIR) means how many more good reps you could have done when you ended a set. If you stop a set of 5 feeling like you had two more clean reps in you, that's 2 RIR.

RIR is useful because your strength changes from day to day with sleep, stress, food and life in general. On a good day, 80% can feel light. On a rough day, it can feel like a max. Training by RIR lets you adjust to how you actually feel.

Many lifters use percentages to choose a starting weight, then RIR to nudge it up or down. Most working sets end around 1–3 RIR. Newer lifters often underestimate how many reps they have left, so filming a set can help you calibrate.

How often to re-estimate

Beginners tend to gain strength quickly, so an estimate can be out of date within a few weeks. Re-check every 4–6 weeks, or sooner if your working sets start to feel clearly easier. More experienced lifters progress more slowly and can usually re-estimate every couple of months or at the end of a training block.

You don't need a special test day. Just enter any hard, clean set of 3–8 reps from normal training. If the estimate keeps creeping up, you're making progress.

Why estimates differ between people and exercises

Rep-max formulas assume everyone loses reps at the same rate as the weight goes up. In reality, people and lifts vary:

• Muscle endurance. Some people can grind out many reps close to their max, while others drop off quickly. Someone with a lot of endurance training may get more reps at a given weight, which can make a high-rep estimate come out too high.
• Experience. Newer lifters have had less practice with heavy weights and less consistent technique, so their true single-rep max may be lower than an estimate suggests.
• The exercise itself. People often manage more reps at the same percentage on big lower-body lifts than on the bench press. Small isolation exercises and many machines don't follow the formulas well at all.

So estimate each lift separately, and adjust if the percentages feel much too heavy or light after a session or two.

Lifting heavy safely

• Warm up with several gradually heavier sets before your hardest set. Here's how to warm up before exercise.
• Set safety bars or pins in a rack for squats and bench presses, or use a spotter who knows what to do. Never bench heavy alone without safeties.
• If you're a beginner, skip true max testing. Spend your first months learning technique with moderate weights. An estimate is all you need.
• Stop the set if you feel sharp pain, get dizzy, or your form breaks down. The strain of hard effort is normal, but pain is not.
• Heavy lifting, especially when you hold your breath, briefly raises blood pressure. If you have a heart condition, high blood pressure, a recent injury, are pregnant, or haven't exercised in a long time, talk to a doctor or physical therapist before lifting heavy.

Strength training works best alongside enough food and protein to recover. The protein calculator and calorie calculator can help you set sensible starting points.

Based on: Epley (1985) and Brzycki (1993) formulas.