One-Rep Max Calculator
Estimate your one-rep max (1RM) for any lift using the Epley formula based on weight and reps performed.
This free online one-rep max calculator provides instant results with no signup required. All calculations run directly in your browser — your data is never sent to a server. Enter your values below and see results update in real time as you type. Perfect for everyday calculations, homework, or professional use.
Range: 1 – 1000
The weight you lifted (use any unit consistently).
Range: 1 – 30
Number of reps completed with good form.
Results
Estimated 1RM
116.7
90% (2-3 reps)
105
80% (7-8 reps)
93.3
70% (12-15 reps)
81.7
How to Use This Calculator
Enter your input values
Fill in all required input fields for the One-Rep Max Calculator. Most fields include unit selectors so you can work in your preferred unit system — metric or imperial, whichever matches your problem.
Review your inputs
Double-check that all values are correct and that you have selected the right units for each field. Incorrect units are the most common source of calculation errors and can produce results that are off by factors of 2, 10, or more.
Read the results
The One-Rep Max Calculator instantly computes the output and displays results with units clearly labeled. All calculations happen in your browser — no loading time and no data sent to a server.
Explore parameter sensitivity
Try adjusting individual input values to see how the output changes. This is a quick and effective way to develop intuition about how different parameters influence the result and to identify which inputs have the largest effect.
When to Use This Calculator
- •Use the One-Rep Max Calculator when you need accurate results quickly without the risk of manual computation errors or unit conversion mistakes.
- •Use it to verify calculations made by hand or in spreadsheets — an independent check can catch errors before they lead to costly decisions.
- •Use it to explore how changing input parameters affects the output — a quick way to develop intuition and identify the most influential variables.
- •Use it when collaborating with others to ensure everyone is working from the same numbers and applying the same assumptions.
About One-Rep Max Calculator
Your one-rep max (1RM) is the heaviest weight you can lift for a single repetition with proper form. It is the foundation of percentage-based strength training programs, which prescribe working weights as percentages of 1RM. Directly testing your 1RM requires careful preparation, spotters, and carries injury risk, so most lifters use estimation formulas instead. The One-Rep Max Calculator uses the Epley formula, one of the most widely validated 1RM prediction equations, to estimate your max from a submaximal set. Simply enter the weight you lifted and how many reps you completed, and the calculator produces your estimated 1RM along with common training percentages. This information helps you program strength, hypertrophy, and endurance phases of training.
The Math Behind It
Formula Reference
Epley Formula
1RM = Weight x (1 + Reps / 30)
Variables: Weight = weight lifted; Reps = number of repetitions completed; valid for 1-10 reps
Worked Examples
Example 1: Squat: 100 kg for 5 reps
A lifter squats 100 kg for 5 reps.
Estimated 1RM is approximately 117 kg. Training weights: 105 kg at 90%, 93 kg at 80%, 82 kg at 70%.
Common Mistakes & Tips
- !Using reps above 10 for prediction; accuracy decreases significantly beyond 10 reps.
- !Not using strict form for the rep test; cheat reps inflate the estimate.
- !Applying upper-body 1RM formulas to lower-body exercises or vice versa without adjustment; the relationship between reps and max differs by muscle group.
Related Concepts
Used in These Calculators
Calculators that build on or apply the concepts from this page:
Frequently Asked Questions
How accurate is the Epley formula?
Within about 5 percent for sets of 1-6 reps. Accuracy decreases with higher rep counts. For the most precise estimate, use a set of 3-5 reps.
Should I ever test my actual 1RM?
Direct testing is useful for powerlifting competition preparation but carries injury risk. Most recreational lifters should rely on estimated 1RM from submaximal sets.