One-Rep Max (1RM) is the maximum amount of weight you can lift for a single repetition of a given exercise with proper form. It's a key metric in strength training used to measure progress, design training programs, and set appropriate working weights. Rather than testing your actual 1RM (which can be risky), you can estimate it using submaximal lifts and mathematical formulas.

Knowing your 1RM allows you to calculate percentages for different training goals: strength work typically uses 85-95% of 1RM, hypertrophy (muscle building) uses 70-85%, and muscular endurance training uses 50-70%. This calculator uses proven formulas developed by sports scientists to give you reliable estimates without the risk of maximal testing.

Epley Formula: The most widely used formula, particularly effective for rep ranges of 1-10. It assumes a linear relationship between weight and repetitions.

Brzycki Formula: Often considered most accurate for lower rep ranges (1-6). It tends to give slightly lower estimates than Epley for higher rep ranges.

Lander Formula: Provides a good middle ground and works well across moderate rep ranges (3-10 reps).

Lombardi Formula: Uses an exponential calculation and may be more accurate for experienced lifters with consistent form.