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Rep Max Conversion Calculator

Turn one rep max into the load for any target rep count.

Result

106.06
116.67

How it is calculated

The tool converts a set you have done into the weight you could use for a different rep count, using the Epley formula in two steps. First it estimates the one-rep max: 1RM = w × (1 + r/30), where w is the weight lifted and r the reps you did. Then it solves the formula backwards for the target rep count n: W(n) = 1RM / (1 + n/30). At exactly 1 rep the formula is not applied: a single rep is taken as the one-rep max itself, so 100 for 1 rep gives 1RM 100.00. Reps and target reps must be whole numbers from 1 to 20 (5.5 or 21 give no result), and the weight must be above zero. Answers are in the same unit as your weight, to two decimals. The estimate assumes the original set was taken close to failure.

Worked example

You lifted 100 for 5 reps and want the weight for 3 reps. Step 1: 1RM = 100 × (1 + 5/30) = 100 × 1.1667 = 116.67. Step 2: W(3) = 116.67 / (1 + 3/30) = 116.67 / 1.1, which is 106.06. The tool shows 116.67 as the estimated one-rep max and 106.06 as the target weight. In the other direction, for 12 reps the same set gives 116.67 / 1.4, or 83.33.

Try this example →

Common mistakes

  • Starting from a set that was not near failure. If you could have done 3 more reps, the 1RM and every converted weight come out too low.
  • Converting across a big gap, such as a 3-rep set to a 20-rep target. The linear Epley model drifts away from real performance at high reps, so treat 15 to 20 reps as rough.
  • Swapping the two rep fields. Reps is what you did, target reps is what you want to plan; reversed, the weight moves in the wrong direction.
  • Typing a fraction of a rep such as 5.5. Reps must be whole numbers; a fractional count gives no result.
  • Expecting the weight to match a Brzycki table. Only Epley is used, so a chart based on Brzycki will give slightly different loads.

Sources

About this calculator

A rep max is the heaviest weight you can lift for a given number of repetitions, and strength-training formulas let you convert a known rep max at one rep count into an estimated load at any other. One of the most widely used is the Epley formula, 1RM = weight × (1 + reps/30); this calculator uses Epley (a single rep is taken as your 1RM as is, and reps are whole numbers from 1 to 20) and applies the relationship in reverse to solve for the weight you should be able to lift at your target rep count, not just your theoretical one-rep max.

Powerlifters and strength coaches rely on this conversion to program percentage-based training without constantly testing a true 1RM, which carries injury risk and fatigue cost — instead, they test a comfortable 5RM or 3RM and derive the rest of the training percentages from it. It’s also how programs prescribe “work up to your 8RM” or similar rep-range targets when an athlete’s most recent max was measured at a completely different rep count.

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