Health & Fitness
One Rep Max (1RM) Calculator
Calculate the maximum weight you can lift for a single repetition based on your performance with lighter weights.
Reviewed by the calculator.uk.com Team · Last reviewed 12 June 2026 · Our methodology
Enter weight and reps to calculate your one rep max
Related to One Rep Max Calculator
The One Rep Max (1RM) Calculator uses multiple scientifically validated formulas to estimate the maximum weight you can lift for a single repetition of an exercise. By inputting the weight you can lift for multiple repetitions, the calculator predicts your 1RM using four different formulas and provides an average estimate.
Calculation Methods
The calculator employs four widely-used formulas in strength training: - Brzycki Formula: 1RM = weight × (36 / (37 - reps)) - Epley Formula: 1RM = weight × (1 + 0.0333 × reps) - Lander Formula: 1RM = (100 × weight) / (101.3 - 2.67123 × reps) - Lombardi Formula: 1RM = weight × (reps)^0.10
The calculator provides both individual estimates from each formula and an average 1RM prediction. The results help you understand your maximum strength potential without actually attempting a one-rep maximum, which can be risky without proper preparation.
Understanding the Rep Max Chart
The Rep Max Chart shows estimated maximum weights for different rep ranges based on your calculated 1RM. This helps you plan your training loads for different rep ranges and understand the relationship between weight and repetitions.
1. What is a One Rep Max (1RM)?
A One Rep Max is the maximum amount of weight you can lift for a single repetition of an exercise with proper form. It's a key measure of strength and is often used to plan training programs and track progress.
2. Why use a calculator instead of testing 1RM directly?
Testing your actual 1RM can be dangerous without proper preparation and supervision. Using a calculator to estimate your 1RM based on submaximal weights is safer and still provides valuable information for training purposes.
3. How accurate are the 1RM predictions?
The accuracy of 1RM predictions typically decreases as the number of repetitions increases. For best results, use a weight that you can lift for 1-5 repetitions. The calculator provides multiple formulas and an average to improve accuracy.
4. How often should I test my 1RM?
Most strength coaches recommend testing or estimating your 1RM every 8-12 weeks. This allows enough time for significant strength gains while providing regular feedback on your progress.
5. What is the scientific source for this calculator?
This calculator uses four long-standing regression formulas for estimating 1RM from a submaximal lift: the Brzycki formula (Brzycki M, 1993, Strength and Conditioning Journal), the Epley formula (developed by strength coach Boyd Epley), and the Lander and Lombardi formulas, both established alternatives used throughout strength and conditioning practice. All four have been compared against each other in exercise-science research, including studies published in the Journal of Strength and Conditioning Research, and each tends to lose accuracy above roughly 10 reps — which is why submaximal tests in the 1-5 rep range give the most reliable estimate.