onerepcalculator
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Hack Squat One Rep Max Calculator

Estimate your one-rep max from a set you have completed. Then see helpful training percentages and a second formula for comparison.

✓ Pounds or kilograms✓ Instant estimates✓ No account

YOUR LIFT

Calculate your one-rep max

Enter the weight you lifted and the number of clean reps you completed.

1RM
Weight unit

How to do the hack squat

Keep your back supported and lower only as far as comfortable.

This calculator uses the total external load you enter. For dumbbell exercises, use the weight per dumbbell and be consistent when comparing workouts. For machine exercises, keep the same machine and setup, because stacks and leverage differ.

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UNDERSTAND YOUR RESULT

What is a one-rep max?

Your one-repetition maximum (1RM) is the greatest weight you can lift once with proper form for a particular exercise. You can estimate it without attempting a heavy single: enter the weight and reps from a challenging set.

Our default estimate uses the Epley formula. We also show the Brzycki estimate so you can see that there isn't one exact formula for every lifter. The estimates become less dependable as repetitions rise, especially if the set wasn't close to your actual limit.

How accurate is a 1RM calculator?

It's a useful starting point for planning, not a guarantee of what you can lift. Rep technique, training experience, fatigue, equipment, and proximity to failure all matter. Use a recent, consistent set, ideally around 3–6 hard repetitions, and never treat the result as a reason to attempt an unsafe maximum.

Read our calculation methodology →

Strength starts with a good baseline.

Calculate a reliable starting estimate and build your next workout from there.

Calculate your 1RM ↗