🏋️ One Rep Max Calculator

Estimate your one-repetition maximum (1RM) — the most weight you can lift for a single rep — using four validated strength formulas: Epley, Brzycki, Lombardi, and Mayhew. Enter the weight you lifted and how many reps you completed to get your estimated 1RM and a full training percentage table.

Weight lifted (kg)

Reps performed (1–30)

Estimated 1RM (Average)

—

Epley

—

Brzycki

—

Lombardi

—

Mayhew

Training Percentage Table

% of 1RM	Weight	Est. Reps

1RM Formulas

Epley: 1RM = weight × (1 + reps / 30)

Brzycki: 1RM = weight × 36 / (37 − reps)

Lombardi: 1RM = weight × reps^0.10

Mayhew: 1RM = 100 × weight / (52.2 + 41.9 × e^{−0.055 × reps})

The Epley formula is the most widely used and generally performs well across all rep ranges. The Brzycki formula is particularly accurate for lower rep ranges (1–10) but becomes invalid above 36 reps. The average of all four formulas provides the most robust estimate.

How to Use the One Rep Max Calculator

1

Select Your Unit System

Choose metric (kg) or imperial (lbs) depending on the unit your equipment uses. The results will display in the same unit.
2

Enter the Weight Lifted

Enter the load you used for your set. Use the actual weight on the bar including any plates.
3

Enter Reps Performed

Enter how many reps you completed with that weight. For best accuracy, aim for 3–10 reps — estimates become less reliable above 10 reps.
4

Read Your 1RM and Table

See your estimated 1RM from four formulas plus the average. Use the training percentage table to plan your working weights for different goals.

Example Calculation

A lifter completes 5 reps with 100 kg:

Epley: 100 × (1 + 5/30) = 116.7 kg

Brzycki: 100 × 36/(37−5) = 112.5 kg

Lombardi: 100 × 5^0.10 = 117.5 kg

Mayhew: 100×100/(52.2+41.9×e^(−0.275)) ≈ 117.9 kg

Average 1RM = 116.2 kg

Frequently Asked Questions

What is One Rep Max (1RM)?

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 is the gold standard measure of strength and is used to prescribe training loads as a percentage of 1RM. Testing your true 1RM directly is possible but carries injury risk, so the formulas in this calculator provide a safe estimate from a sub-maximal set.

Which formula is most accurate?

No single formula is universally best — accuracy depends on the individual and the rep range used. The Epley formula is the most widely cited and performs consistently across rep ranges. Brzycki is highly accurate for 1–10 reps. For the most reliable estimate, this calculator averages all four formulas. Always treat the result as an estimate and approach true maximal attempts with caution.

How often should I test my 1RM?

For most lifters, testing or estimating 1RM every 4–8 weeks is sufficient to track progress. Beginners often improve quickly enough to re-test monthly. Advanced lifters may test less frequently. Rather than performing true 1RM attempts regularly, many coaches recommend estimating 1RM from a 3–5 rep set every training cycle for safety and recovery reasons.

What if I perform more than 10 reps?

The accuracy of all 1RM estimation formulas decreases significantly beyond 10 reps. At higher rep counts, the relationship between reps and maximum strength becomes less predictable because muscular endurance plays a larger role. For the most accurate estimate, choose a weight that limits you to 3–6 reps. Results from sets of 15+ reps should be treated as rough approximations only.