| % of 1RM | Weight ('+unit+') | Approx. Reps |
|---|---|---|
| '+percents[i]+'% | '+val+' '+unit+' | '+repApprox[i]+' |
Calculator Use
The 1 rep max calculator is an essential tool for weightlifters, powerlifters, and fitness enthusiasts to estimate the maximum amount of weight they can lift for a single repetition of a given exercise. Testing your true one-rep max (1RM) can be physically taxing and potentially dangerous without proper spotting and preparation. This calculator allows you to predict that limit safely using sub-maximal efforts.
To use this tool, perform a set of an exercise (like the bench press, squat, or deadlift) with a weight you can handle for 2 to 10 repetitions. Enter those numbers above to see your estimated maximum.
- Weight Lifted
- The amount of resistance used in your sub-maximal set (in pounds or kilograms).
- Repetitions
- The total number of completed, high-quality reps performed before reaching technical failure.
- Estimation Formula
- Different mathematical models used to predict the 1RM. Brzycki and Epley are the industry standards.
How It Works
When you lift a weight multiple times, your muscles fatigue at a predictable rate. Exercise scientists have mapped this fatigue to create formulas that back-calculate your absolute strength. The most common formula used in this 1 rep max calculator is the Brzycki Formula:
1RM = Weight / (1.0278 – (0.0278 × Reps))
- Weight: The load on the bar.
- Reps: The number of times the load was moved through a full range of motion.
- Constants: 1.0278 and 0.0278 are statistical coefficients derived from athlete testing.
Calculation Example
Example: A lifter performs 5 repetitions of the back squat with 225 lbs and wants to know their estimated 1RM using the Brzycki method.
Step-by-step solution:
- Weight = 225
- Reps = 5
- Calculate denominator: 1.0278 – (0.0278 × 5) = 1.0278 – 0.139 = 0.8888
- Divide weight by denominator: 225 / 0.8888
- Result = 253.1 lbs
Common Questions
How accurate is a 1 rep max calculator?
The accuracy is highest when the repetitions performed are between 2 and 6. As the number of reps increases (above 10), individual differences in muscular endurance make the prediction less reliable. For most lifters, the result is within 3-5% of their actual capacity.
Which formula is the best?
The Brzycki formula is widely considered the most accurate for lower-rep ranges (under 10), while the Epley formula is often preferred for compound movements like the deadlift. Most lifters find the results between formulas to be very similar.
Why should I know my 1RM?
Knowing your 1RM is crucial for following structured strength programs. Most programs prescribe intensity as a percentage (e.g., "perform 3 sets of 5 at 80% of your 1RM"). Without an accurate estimate, you may be training too light to stimulate growth or too heavy to recover.