1RM Calculator

Find out how much weight you could lift for a single rep - without the risk of testing a true max. Enter a weight you've lifted and the number of reps you hit, and the calculator will estimate your 1RM using proven strength formulas.

What Is a One Rep Max?

Your one rep max (1RM) is the heaviest weight you can lift for a single repetition of an exercise with good form. It's the standard way lifters measure strength on the big movements like the squat, bench press, deadlift, and overhead press.

Knowing your 1RM is useful because most strength programs tell you what to lift as a percentage of it — for example, "work up to 5 reps at 80%." Once you know your max, you know exactly what to put on the bar.

Testing a true 1RM is taxing and carries some injury risk, especially if you're newer to lifting or training alone. That's where this calculator comes in. Instead of grinding out a true max, you do a lighter set you can handle for a few clean reps, and the math fills in the rest.

How the Calculator Works

Enter two things:

1. The weight you lifted (in kg or lbs)
2. The number of reps you completed with good form

The calculator runs those numbers through a well-tested strength formula to estimate your 1RM. A few different formulas exist (Epley and Brzycki are the most common), and they agree closely when you're working in the 3–6 rep range.

For the curious: the Epley formula is simply weight × (1 + reps / 30). So 100 kg for 5 reps estimates a 1RM of about 117 kg. Other formulas use slightly different math but land in the same neighborhood.

Getting an Accurate Estimate

The result is only as good as the set you put in. A few things help:

• Stay in the 2–10 rep range, ideally 3–6. Formulas are most accurate at lower reps. Above 10 reps, estimates drift and endurance becomes a bigger factor than strength.
• Take the set close to failure. If you stop at 5 reps but could have done 10, the estimate will come out way too low. Aim for a set where the last rep is genuinely hard.
• Use strict form. Half-reps, bouncing, and heavy momentum skew the result and don't reflect real strength.
• Rest properly before the set. Give yourself 3–5 minutes after your last warm-up so you can put in a true effort. Don't test at the end of a long workout.
• Pick a big lift. 1RM estimates are most meaningful on movements that use a lot of muscle at once — squats, bench, deadlifts, and presses. You can use it for curls or other isolation exercises, but the number won't be as useful for planning training.

Using Your 1RM to Plan Training

Once you have an estimated 1RM, you can use it to pick weights for whatever you're training for:

Note: hypertrophy actually works across a wide range of loads — roughly 30–85% of 1RM — as long as your sets are taken close to failure. The 6–12 zone is just the classic, time-efficient sweet spot.

For example, if your estimated bench 1RM is 100 kg and you're training for muscle growth, you'd work in the 65–80 kg range for sets of 6–12.

Retest every 4–8 weeks. As you get stronger, your percentages shift. Plugging a new set into the calculator every month or two keeps your training weights aligned with your actual capacity.

Things to Keep in Mind

• It's an estimate, not a guarantee. Predicted 1RMs are usually within about 5–10% of a true max for low-rep sets on compound lifts, but error grows with higher reps and varies by exercise (bench and overhead press tend to be less predictable than squat or deadlift).
• Your result varies by lift. Experience with the specific lift matters — the more familiar you are with the movement, the closer your estimate will be.
• Fatigue and stress affect the number. Sleep, nutrition, and how hard you trained yesterday all influence what you can do today. One bad day doesn't mean you lost strength.
• Technique trumps the number. A clean, controlled rep at a lower weight beats an ugly, grinding rep at a higher one — both for progress and for staying healthy.

Common Questions

How accurate is a 1RM calculator?

For low-rep sets (3–6 reps) on big compound lifts, estimates are typically within 5–10% of a real max. Accuracy drops as reps climb, and calculators work better for experienced lifters than beginners (whose technique and effort vary more set to set).

Which 1RM formula is most accurate?

No single formula wins across the board. Epley and Brzycki are the most widely used and agree closely below 10 reps. Different formulas perform slightly better on different lifts and populations — the differences are usually smaller than the normal day-to-day variation in your own performance, so picking one and sticking with it is fine.

Should beginners test their 1RM?

Not really. In your first several months of lifting, your strength is going up fast enough that any max test is out of date within weeks. Form also breaks down more under maximal loads when you're still learning a movement. Use the calculator with a 5–8 rep set instead — it's safer, and the number will be just as useful.

How often should I recalculate?

Every 4–8 weeks is a good rhythm for most lifters. Newer lifters might retest sooner (strength changes quickly at first); advanced lifters can go longer between recalculations. Whenever a set feels noticeably easier or harder than your programmed percentages suggest it should, it's time to plug in a fresh set.

Can I use this for any exercise?

Yes, but the estimate is most meaningful for compound barbell lifts (squat, bench press, deadlift, overhead press). It still works for dumbbell lifts, pull-ups, and machines, but percentage-based programming is less common outside the main barbell lifts.