Estimate your one-repetition maximum from a weight you lifted for 1 to 20 clean repetitions. Compare seven established 1RM equations, see the spread between formulas and build a percentage-based load table in kilograms or pounds.
- Kilograms and pounds
- Seven 1RM equations
- 50% to 100% load table
- Rep-max projections
One-Rep Max Calculator with Formula Comparison
Enter the load and the number of full, controlled repetitions you completed. The calculator keeps each equation separate, then reports your selected method or the mean of all seven methods.
Bench press, average of seven formulas
Set intensity reference
86.7% of estimateThis percentage describes the entered set relative to the selected formula estimate. It is not a measured intensity or a guarantee of repetitions available.
Formula-by-formula 1RM comparison
| Method | Estimated 1RM | Difference from mean |
|---|
Percentage-based training load table
| % of estimated 1RM | Calculated load | General programming reference |
|---|
Projected repetition loads
| Target reps | Projected load | Approx. % of selected 1RM |
|---|
Projection uses the inverse of the selected equation. “Average” uses the mean inverse ratio of all seven equations.
Recent calculations
Results remain in this page session. The calculator does not send your inputs anywhere.
How to Use This One-Rep Max Calculator
- Select kilograms or pounds. Use the same unit shown on the bar, dumbbell, machine or training log.
- Select the exercise. The exercise name labels your result; it does not silently change an equation.
- Enter the load and the number of clean repetitions completed in one continuous set. Enter 1 only when the entered weight was a successful single.
- Choose the average or one named formula. The average reduces dependence on one equation, while the comparison table keeps the disagreement visible.
- Select a practical rounding increment. For example, 2.5 kg suits many barbells, while 5 lb often suits equipment loaded in pounds.
- Review the primary estimate, formula range, percentage table and rep projections. Use the estimate for planning, not as proof you should attempt the predicted maximum.
For a useful comparison over time, repeat the same exercise with similar technique, equipment, range of motion and fatigue conditions. A bench press result does not transfer directly to a chest-press machine, and a high-bar squat result is not interchangeable with a leg-press result.
What Is a One-Rep Max?
A one-repetition maximum, written as 1RM, is the heaviest load a person can lift once through the required range of motion with acceptable technique. Coaches use 1RM as a reference for maximal dynamic strength and for expressing training load as a percentage. A direct 1RM test involves progressively heavier single attempts. An estimated 1RM uses a submaximal set and a prediction equation.
Estimation is convenient when a true maximal attempt is unsuitable, unnecessary or difficult to organize. It also produces less specific information. Repetition performance varies with the exercise, lifting tempo, pause rules, equipment, training history, fatigue and willingness to approach failure. Treat the output as a planning value tied to the entered set.
One-Rep Max Formulas Used
Each formula uses w for the lifted weight and r for completed repetitions. The unit does not affect the mathematics, so the same equation works with kilograms or pounds. When repetitions equal 1, this calculator treats the entered successful single as the 1RM instead of allowing an equation to inflate it.
The “average of seven” option calculates all seven estimates and takes their arithmetic mean. It does not claim seven independent measurements or create a statistical confidence interval. The displayed formula range is the lowest through highest equation result for the same set.
Worked 1RM example
Suppose you bench press 100 kg for 5 controlled repetitions. The Epley equation gives 100 × (1 + 5 ÷ 30) = 116.67 kg. The Brzycki equation gives 100 × 36 ÷ (37 − 5) = 112.50 kg. Other equations return their own estimates. The calculator displays every result and uses their mean when the average method is selected. If the average is about 115 kg, an 85% reference load is 115 × 0.85 = 97.75 kg, then rounded to the increment you selected.
How the Seven Formulas Differ
| Formula | Mathematical pattern | How to use the result |
|---|---|---|
| Epley | Linear increase with each added repetition | Common general estimate; tends to rise steadily at higher reps |
| Brzycki | Fraction based on repetitions remaining below 37 | Common lower-rep comparison; often more conservative than Epley below 10 reps |
| Lander | Linear denominator | Useful as a separate published estimate, not a universal correction |
| Lombardi | Power relationship | Responds differently as repetitions rise |
| Mayhew | Exponential relationship | Originally associated with bench-press prediction work |
| O'Conner | 2.5% increase per repetition | Simple and often conservative |
| Wathen | Exponential relationship | Adds another established model to the comparison |
Research does not identify one formula as the most accurate for every person and every exercise. A 2024 study comparing equations across bench press, squat and arm curl found that performance differed by lift and participant group. This is why the calculator shows the formula spread instead of hiding it behind one precise-looking value.
How Repetition Count Affects Accuracy
Lower-repetition sets usually resemble a maximum-strength task more closely. As repetitions increase, local muscular endurance, pacing, technique and tolerance of discomfort have more influence. The calculator accepts up to 20 repetitions so you can inspect a result, but it displays a clear warning above 10 and a stronger warning above 15.
- 1 rep: the entered successful single is used directly. It is not a prediction.
- 2 to 5 reps: a lower-repetition estimate with less extrapolation from the completed set.
- 6 to 10 reps: a practical estimate, with more room for exercise and endurance differences.
- 11 to 15 reps: a wider-uncertainty estimate. Compare formulas and avoid treating decimals as certainty.
- 16 to 20 reps: a low-confidence projection. Consider collecting a controlled lower-repetition set if appropriate.
A set must also be challenging enough to inform a repetition-maximum estimate. If you stop with many repetitions still available, equations will underestimate what you might lift once. Do not create fatigue or sacrifice form merely to improve the estimate.
Using Percentage-Based Training Loads
The percentage table multiplies the selected 1RM estimate by values from 50% to 100%. These are arithmetic reference loads. They do not prescribe sets, repetitions, rest periods or weekly volume. Individual repetition capacity at a given percentage varies, and the number changes across exercises.
For example, if your selected estimate is 120 kg, then 80% is 96 kg and 70% is 84 kg. With rounding set to 2.5 kg, those display as 95 kg and 85 kg. Rounding should reflect equipment you can load safely. Dumbbells, fixed machines and specialty bars may require different increments.
Update percentages when a repeatable performance change occurs. Recalculating from every unusually good or poor session creates noise. Track the exercise, equipment, set, date and technique standard alongside the estimate.
Estimated 1RM Versus a Direct 1RM Test
| Point | Estimated 1RM | Direct 1RM test |
|---|---|---|
| Input | A submaximal load and completed reps | The heaviest successful single |
| Output | Equation-based projection | Observed performance under test conditions |
| Setup | Fits a normal training set | Needs progressive attempts, rest and safety planning |
| Main limitation | Formula and endurance differences | Fatigue, skill, attempt selection and test-day readiness |
| Best comparison | Same equation and conditions over time | Same protocol, equipment and judging standard over time |
The NSW Agency for Clinical Innovation describes a 1RM as the highest load lifted once through full range of motion with good form. Its testing guide also emphasizes screening, breathing, positioning, consistent equipment settings and stopping when the required range or technique is lost. The Human Performance Resources Center outlines progressive warm-up attempts, rest periods and load adjustments for direct testing.
Safety and Testing Considerations
- Use stable equipment, collars, pins, safeties or a trained spotter where the exercise requires them.
- Warm up progressively. A calculator result does not replace exercise-specific preparation.
- Do not test through pain, dizziness, unusual shortness of breath or loss of technique.
- Do not use another person’s estimate or a result from a different exercise as your starting maximum.
- Seek qualified guidance if you are new to lifting, returning after injury, pregnant, managing a medical condition or unsure whether maximal exertion is appropriate.
- For youth athletes, older adults and clinical populations, use age-appropriate supervision and screening rather than a generic maximal-testing plan.
Common 1RM Calculator Mistakes
- Entering the total weight on one side of a barbell instead of the full loaded weight, including the bar.
- Mixing kilograms and pounds. One kilogram equals about 2.20462 pounds.
- Counting assisted, shortened or technique-altered repetitions as equivalent full repetitions.
- Using a set stopped far from fatigue, then reading the result as a true maximum.
- Comparing estimates from different formulas without noting the method.
- Assuming a formula range is a statistical confidence interval.
- Attempting the calculated maximum despite inadequate setup, skill or recovery.
- Rounding to a load the available equipment cannot produce safely.
How to Collect a More Repeatable Input Set
Prediction quality starts before you enter a number. Record the full exercise setup, including the bar or machine, grip or stance, range of motion and any pause requirement. Use the same setup when you repeat the calculation. A wider grip, shortened depth, lifting straps, a different machine or a change from touch-and-go to paused repetitions can change performance even when the exercise name looks unchanged.
Complete a consistent warm-up that prepares you without creating unnecessary fatigue. Then choose a load you expect to lift for a low or moderate number of controlled repetitions. The final counted repetition should meet the same technique standard as the first. If a spotter touches the bar, the set no longer represents an unassisted repetition maximum at that load.
Session conditions also matter. Sleep, prior training, rest between sets, pain, motivation and exercise order can move the result. One estimate should not define your strength. Look for a trend across comparable sessions. If 100 kg for 5 reps becomes 100 kg for 7 reps under the same conditions, the calculated change is more informative than comparing unrelated exercises or different formula settings.
Keep unrounded values for tracking and round only the load you plan to place on equipment. The calculator follows this rule internally. It calculates with full precision, then applies your selected equipment increment to displayed results. This avoids compounding early rounding through the percentage and rep-projection tables.
Calculation Method and Review Sources
The definition and direct-testing precautions were reviewed against the NSW Agency for Clinical Innovation 1RM guide. General direct and multiple-repetition testing guidance was checked against the Human Performance Resources Center 1RM overview.
Formula limitations and exercise-specific differences were reviewed against LeSuer and colleagues’ equation-comparison study and a 2024 comparison across three lifts. Source review supports transparent estimation; it does not make the output an individualized training prescription.
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Frequently Asked Questions
How do I calculate my one-rep max?
Enter a weight and the number of clean repetitions completed. A prediction equation converts the submaximal set into an estimated single. This tool compares seven equations and lets you use one formula or their mean.
Which 1RM formula is most accurate?
No formula is most accurate for every lift and person. Accuracy changes with the exercise, repetition count, training status and testing method. Compare the formula range and use the same method when tracking change.
How accurate is a one-rep max calculator?
It provides an estimate, not a measured maximum. Lower-repetition sets generally require less extrapolation, while higher-repetition sets are more affected by muscular endurance and pacing. Exercise and individual differences remain at every rep count.
How many reps should I use to estimate 1RM?
A challenging set of about 2 to 10 controlled reps is commonly used. Estimates from more than 10 reps carry more uncertainty. The calculator accepts up to 20 reps but warns when extrapolation becomes wider.
Does the calculator work for kilograms and pounds?
Yes. The equations multiply the entered load, so they work in either unit. Keep one unit throughout the calculation. The tool converts the current weight when you switch between kilograms and pounds.
Why do the seven formulas give different results?
They model the relationship between load and repetitions with different linear, fractional, power or exponential equations. The disagreement shows model uncertainty and should remain visible rather than being presented as false precision.
Is an estimated 1RM the weight I should attempt?
No. It is a programming reference. A maximal attempt also depends on experience, technique, warm-up, recovery, equipment, safeties, spotting and health considerations.
Why is my completed set shown as a percentage of 1RM?
The calculator divides the lifted weight by the selected estimated 1RM. The result helps describe the set relative to the estimate. It does not guarantee a specific number of repetitions at that percentage.
Strength and Calculation Disclaimer
This calculator provides an educational estimate from the information you enter. It does not assess technique, readiness, injury risk or medical suitability and does not replace a qualified coach or healthcare professional. Do not attempt a maximal lift solely because a formula produced the number.