One Rep Max (1RM) Calculator
Estimate your one rep max without actually attempting it. Enter the weight you lifted and how many reps you did, and get your 1RM based on three proven formulas (Brzycki, Epley, Lander) plus a percentage chart for programming your training.
Best accuracy at 3-10 reps
About the One Rep Max (1RM) Calculator
The One Rep Max (1RM) Calculator on ToolHaven is a free, browser-based tool that helps you estimate your one rep max without actually attempting it. Enter the weight you lifted and how many reps you did, and get your 1RM based on three proven formulas (Brzycki, Epley, Lander) plus a percentage chart for programming your training. It runs entirely in your browser, so no data is sent to any server, and no account or signup is required. Whether you are a student, professional, or just someone looking for a quick answer, this tool gives you accurate results in seconds.
How to use the One Rep Max (1RM) Calculator
Using this tool is straightforward. Enter the weight you lifted and how many reps you completed. Pick your unit (kg or lbs). Hit Calculate to see your estimated 1RM from three formulas. Use the percentage table below to set weights for different rep ranges in your training.
Results are updated instantly as you enter values, so there is no need to click a submit button. You can adjust inputs freely and compare different scenarios in real time.
Why use ToolHaven?
ToolHaven offers 178+ free online calculators and tools across categories including Finance, Health, Math, Education, and more. All tools are free to use, require no installation, and work on any device. Your inputs never leave your browser, so your data stays private. The One Rep Max (1RM) Calculator is part of our Health collection. Explore related tools in the sidebar to get more done in one place.
How to use
- Enter the weight you lifted and how many reps you completed.
- Pick your unit (kg or lbs).
- Hit Calculate to see your estimated 1RM from three formulas.
- Use the percentage table below to set weights for different rep ranges in your training.
Related tools:
Your one rep max (1RM) is the maximum weight you can lift for exactly one complete repetition with proper form. It's the foundation for programming strength training - most programs prescribe loads as a percentage of 1RM (e.g. '5 sets of 3 at 85%'). Rather than testing your true 1RM (which is physically demanding and risks injury), you can estimate it from a submaximal set.
Three commonly used formulas are Brzycki (best for low rep counts), Epley (most widely used), and Lander. Each uses the weight lifted and reps performed to back-calculate an estimated maximum. The average of all three tends to be the most reliable single number to use for programming.
Frequently Asked Questions
Which formula is most accurate?
At low reps (1-6), all three formulas are fairly close. Brzycki tends to be slightly more accurate in this range. At higher reps (10+), accuracy drops for all formulas because fatigue, endurance, and form all start to affect the result more than raw strength.
How do I use the 1RM for training?
Most strength programs express loads as percentages of 1RM. Hypertrophy work is typically 65-75%, strength work 80-90%, and power work 85-95% for low reps. The percentage chart in the calculator gives you specific weights for each range.
How often should I test/recalculate my 1RM?
Every 4-8 weeks is reasonable, or at the end of a training cycle. As you get stronger, your training weights should increase accordingly. You don't need to max out - just do a heavy set of 3-5 reps and recalculate.
Should I attempt my actual 1RM?
Only if you're experienced, have a trained spotter, and know what you're doing. Maxing out frequently is hard on your joints and nervous system. Most lifters test their true 1RM only for competitions or once or twice a year.