One Rep Max Calculator

What is a one rep max?

Your one rep max (often written as 1RM) is the heaviest weight you can lift for a single, complete repetition with good form. If you can squat 140 kg once, but not 145 kg, your squat 1RM is 140 kg.

Lifters, coaches and physiotherapists use the 1RM as a simple way to measure strength. It answers two useful questions:

• How strong am I right now? Your 1RM is a clear number you can track over months and years.
• How heavy should my training be? Most strength programs are written as percentages of your 1RM, such as "5 sets of 5 at 80%". Without knowing your max, those numbers mean nothing.

The catch is that lifting your true maximum is tiring, takes time to warm up for, and carries more risk than normal training, especially if you're new to lifting. That's why most people estimate their 1RM from a lighter set instead. That's exactly what this calculator does.

How to use this one rep max calculator

You only need one recent, honest set. Here's how to get a good estimate:

1. Choose your lift. Pick Bench Press, Squat, Deadlift, Overhead Press, or Other from the dropdown.
2. Enter the weight you lifted. Use the total weight, including the bar. A standard Olympic barbell weighs 20 kg (about 45 lbs).
3. Enter how many reps you did. Any number from 1 to 12 works, but sets of 2–6 reps give the most accurate results.
4. Pick kg or lbs. The calculator remembers your choice for next time.
5. Read your result. The big number is your estimated 1RM, the average of seven formulas. You'll also see each formula's result, plus the lowest and highest estimate.
6. Check your strength level (optional). Add your bodyweight and gender to see whether your lift is at a Beginner, Novice, Intermediate, Advanced or Elite level.
7. Plan your training. Use the percentage table to find the right weight for your next workout.

Tip: Use a set you took close to failure, where you couldn't have done more than one extra rep. If you stopped at 5 reps but could easily have done 10, the calculator will underestimate your strength.

The 1RM formulas explained simply

Over the years, sports scientists and strength coaches have tested lifters, compared their reps to their real maximums, and turned the results into formulas. Each one looks a little different, but they all do the same job: they take your weight and reps and predict your single best lift.

In the formulas below, w is the weight you lifted and r is the number of reps.

Epley

1RM = w × (1 + r ÷ 30)

Created by strength coach Boyd Epley, this is probably the most popular formula in the world. It adds about 3.3% to the weight for every rep you did. It works well for moderate rep ranges and tends to give slightly higher numbers as reps go up.

Brzycki

1RM = w × 36 ÷ (37 − r)

Developed by Matt Brzycki, this formula is very accurate for low reps (under 10) and is widely used in schools and sports teams. For a single rep it gives exactly the weight you lifted, which makes sense.

Lombardi

1RM = w × r^0.10

The Lombardi formula uses a small power instead of a straight line, so each extra rep adds a little less than the one before. It's simple and tends to sit in the middle of the pack.

Lander and O'Conner

Lander: 1RM = 100 × w ÷ (101.3 − 2.67123 × r)

O'Conner: 1RM = w × (1 + 0.025 × r)

Lander's formula gives results very close to Brzycki's. O'Conner's is the most conservative of the group. It adds only 2.5% per rep, so it usually gives the lowest estimate.

Mayhew and Wathan

Mayhew: 1RM = 100 × w ÷ (52.2 + 41.9 × e^{−0.055 × r})

Wathan: 1RM = 100 × w ÷ (48.8 + 53.8 × e^{−0.075 × r})

These two use a curved (exponential) model, which matches how real lifters tend to fatigue across a set. Mayhew's formula was originally built from bench press data and often gives one of the higher estimates.

Why we use the average

Every formula has its own small bias. Some read a little high, some a little low. Averaging all seven smooths out those differences and gives you a balanced, realistic number. For example, 100 kg for 5 reps gives estimates from 112.5 kg to 119 kg, with an average of about 115.5 kg.

How accurate is a 1RM calculator?

For most people, a good estimate lands within a few percent of their true max, which is accurate enough to plan training. How close you get depends on a few things:

• Number of reps. The fewer reps, the more accurate the estimate. Sets of 2–6 are ideal. Beyond 10 reps, results can be off by 10% or more, because endurance starts to matter as much as strength.
• Effort. The set must be close to your limit. Stopping early leads to a low estimate.
• Your body and experience. Some people are naturally better at heavy singles, others at high reps. Beginners often find their real max is lower than estimated, because lifting a very heavy weight is a skill of its own.
• The exercise. Formulas work best on big barbell lifts like the squat, bench press and deadlift. They're less reliable for machines and small isolation exercises.

Treat your result as a smart starting point, not a promise. Recalculate every few weeks with a fresh set to track your progress.

How to safely test your 1RM in the gym

If you have at least a few months of consistent training and want to know your real max, you can test it directly. Follow these steps to do it safely:

Before you start

• Test when you're fresh and well rested, not after a hard week of training.
• Use a spotter for the bench press, and set the safety bars in a squat rack at the right height.
• Know how to fail safely, such as dropping a squat onto the safety bars or letting a spotter take a bench press.
• Use your calculator estimate to choose your target weights.

A simple warm-up plan

1. Empty bar or light weight for 10 easy reps.
2. About 50% of your estimated max for 5 reps.
3. About 70% for 3 reps.
4. About 80% for 1–2 reps.
5. About 90% for 1 rep.
6. Attempt around 100% of your estimate. If it moves well, add a small amount (2.5–5 kg) and try once more.

Rest 2–5 minutes between the heavier sets. Stop as soon as your form breaks down. A lift with poor form doesn't count, and it's where most injuries happen. Most people need no more than 3 attempts above 90%.

Note: If you're a beginner, have an injury, or have a health condition, skip max testing and stick with the estimate. Talk to a qualified coach or doctor if you're unsure.

How to use 1RM percentages for training

Once you know your 1RM, the percentage table above becomes your training guide. Different percentages build different qualities:

• 85–100% (1–5 reps): Builds maximum strength. Best for experienced lifters, used in small doses.
• 70–85% (6–12 reps): The classic zone for building muscle and general strength.
• 50–70% (12+ reps): Good for technique practice, warm-ups, muscular endurance and lighter recovery days.

An example

Say your estimated bench press 1RM is 100 kg and your program says "4 sets of 8 at 75%". Look at the 75% row: that's 75 kg. Because the table shows about 10 reps are possible at 75%, sets of 8 will feel challenging but leave a rep or two in reserve. That's ideal for steady progress.

As you get stronger, update your 1RM every 4–8 weeks so your training weights keep up with you.