Estimate your one-rep max (1RM) from a weight you lifted and the reps you completed, using the Epley and Brzycki formulas, plus a suggested training weight for any target rep range.
Quick Facts
Method
Epley & Brzycki formulas
Epley: weight x (1 + reps/30). Brzycki: weight x 36 / (37 - reps). Both are most accurate for sets of 10 reps or fewer.
Results
Calculated
Estimated 1RM
—
Average of Epley & Brzycki
Epley formula
—
weight x (1 + reps/30)
Brzycki formula
—
weight x 36 / (37 - reps)
Target-rep training weight
—
Weight for your target reps
Ready
Enter your weight and reps, then press Calculate.
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How to use this calculator
Enter the weight you lifted, how many clean reps you completed, and (optionally) a target rep count for training-weight planning, then click Calculate. The calculator estimates your one-rep max (1RM) using the two most widely used sub-max formulas, Epley and Brzycki, so you do not have to test a true single-rep max to know roughly where it stands. Click Clear to reset all fields and start a new calculation.
Understanding the inputs
Weight lifted is the load on the bar (or machine) for the set you performed. Reps completed should be the number of full, controlled reps you got with that weight while close to failure - the formulas assume the set was hard, not a warm-up. Target reps lets you see what weight would let you complete a different rep count, using your estimated 1RM, which is useful for programming a future workout at a specific rep range.
Interpreting the results
The highlighted card shows the average of the Epley and Brzycki estimates - a reasonable single number to work from. The two formula cards let you compare methods; they usually agree closely for sets of 10 reps or fewer and diverge more at higher rep counts. The target-rep training weight uses your estimated 1RM to back-calculate a practical load for a different number of reps. Estimates are most trustworthy for sets performed near muscular failure with good form; treat them as a planning guide, not a guarantee of what you could lift for one true rep.
Frequently Asked Questions
What is a one-rep max (1RM)?
Your one-rep max is the heaviest weight you can lift for a single complete repetition of an exercise with good form. Testing a true 1RM directly is fatiguing and carries injury risk, so lifters usually estimate it from a lighter set taken close to failure using a formula like Epley or Brzycki.
How does the Epley formula work?
The Epley formula estimates 1RM as weight times (1 + reps / 30). For example, 185 lbs for 5 reps gives 185 x (1 + 5/30) = about 215.8 lbs. It tends to project slightly higher than Brzycki as rep counts increase.
How does the Brzycki formula work?
The Brzycki formula estimates 1RM as weight times 36 / (37 - reps). For 185 lbs at 5 reps that is 185 x 36 / 32 = about 208.1 lbs. Both formulas are close to each other and to a measured 1RM when the set is 10 reps or fewer.
How accurate are these estimates?
Estimation formulas are most reliable for sets of about 1 to 10 reps performed close to muscular failure. Above roughly 12 reps the estimate becomes less precise because endurance, not just strength, starts to influence how many reps you complete. Treat the result as a useful planning number, not an exact max.
Practical Guide for One-Rep Max Calculator - Estimate Your 1RM
One-Rep Max Calculator - Estimate Your 1RM is most useful when the inputs reflect the situation you are actually planning around, not a best-case estimate. Treat the result as a decision aid: it gives you a structured way to compare assumptions, spot outliers, and decide what to verify next. For Sports work, the most important review lens is repeatability, fatigue, recovery, pacing, training load, and conditions on the day.
Start with a baseline run using values you can defend. Then change one assumption at a time and watch which output moves the most. If one input dominates the result, spend your verification time there first. If several inputs have similar influence, use a conservative scenario and an optimistic scenario to create a practical range instead of relying on a single exact number.
Before acting on the result, compare the result with recent sessions, race logs, and coach feedback instead of relying on a single best effort. This is especially important when the calculator supports a purchase, project plan, performance target, or operational decision. The calculator can make the math consistent, but the quality of the conclusion still depends on current data, clear units, and assumptions that match your real constraints.
When the output looks surprising, slow down and inspect each input in order. A small change in one high-leverage field can move the final number more than several low-leverage fields combined. For One-Rep Max Calculator - Estimate Your 1RM, that means you should first confirm the value with the greatest scale, then confirm the value with the greatest uncertainty, then rerun the calculator with conservative and optimistic assumptions. This sequence turns the calculator from a single answer into a practical decision range.
Review Checklist
Confirm every input uses the unit and time period requested by the calculator.
Run a low, expected, and high scenario so the answer has a useful range.
Check whether rounding or a missing decimal place changes the decision.
Update the calculation each training block, after a tune-up event, or when volume and intensity change.