How to Calculate Your One Rep Max (1RM) Safely

To calculate your one rep max (1RM), lift a weight you can handle for 3–8 good reps, then plug the weight and reps into a formula. The most common is Epley: 1RM = weight × (1 + reps ÷ 30). For 100 kg × 5 reps that's about 116.7 kg. The One Rep Max Calculator gives Epley and Brzycki estimates plus a full training-percentage table.

What is a one rep max?

Your 1RM is the heaviest weight you can lift once with good form for a given exercise, such as the squat, bench press or deadlift. Strength programmes use it as a reference: "4 sets of 6 at 80%" means 80% of your 1RM.

How do I estimate my 1RM step by step?

1. Warm up with a few light sets.
2. Pick a weight you think you can lift 3–8 times.
3. Do one hard set with good form, stopping when the next rep would break down.
4. Enter the weight and reps in the One Rep Max Calculator in kg or lb. It accepts 1–12 reps; a single rep is already your 1RM.

Which 1RM formula is best?

The calculator shows two widely used formulas:

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

Example: 100 kg for 5 reps

• Epley: 100 × 1.167 = 116.7 kg
• Brzycki: 100 × 36 ÷ 32 = 112.5 kg

They agree closely at low reps and drift apart at higher reps. Neither is "right" for everyone: people with more fast-twitch muscle often do fewer reps at a given percentage than the formulas predict.

How do I use percentages of my 1RM?

The calculator lists 50% to 100% of your estimated max with typical rep ranges. With an estimated 1RM of 116.7 kg:

% of 1RM	Weight	Typical reps	Common goal
90%	105 kg	about 4	Max strength
80%	93.4 kg	about 8	Strength and size
70%	81.7 kg	about 12	Muscle growth
60%	70 kg	about 20	Technique, endurance

Round to the nearest plate you have. Many programmes base training on a "training max" of about 90% of your estimated 1RM, which leaves room to progress.

Common mistakes when estimating 1RM

• Sloppy reps. Bouncing, cutting depth or lifting the hips off the bench inflates the number.
• Too many reps. Sets of 15+ give unreliable estimates.
• Testing when tired. Do it at the start of a session, after a warm-up.
• Comparing different exercises. A squat 1RM tells you nothing about your bench.
• Re-testing too often. Every 4–8 weeks is plenty.

Is it safe to max out?

Testing a true single can be useful for experienced lifters and competitors, but it's more fatiguing and carries more risk. If you do, use a spotter or safety bars, and stop if your form changes. Beginners get stronger quickly on submaximal work and don't need to test true maxes.

If you have high blood pressure, heart problems or a recent injury, check with a doctor before very heavy lifting and avoid holding your breath for long efforts.

Fuel your training

Strength gains depend on recovery: enough sleep, enough calories and enough protein, typically 1.6–2.2 g per kg of body weight a day for people who lift. Plan it with the Macro Meal Planner and read how to calculate macros for fat loss and muscle. To track whether you're gaining muscle rather than fat, use the Body Fat Calculator.

Estimate your max

Open the free One Rep Max Calculator, choose kg or lb, enter the weight and reps from your last hard set, and use the percentage table to plan your next sessions. It runs in your browser with no sign-up.