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Reps in Reserve Calculator

Use RIR to turn any set into a reliable 1RM estimate.

How it is calculated

The tool adds your reps in reserve to the reps you did, to estimate how many you could have done to failure, then applies the Epley formula: reps to failure = reps + RIR and est. 1RM = weight × (1 + reps to failure / 30). Weight is in kilograms, reps is the number you completed (at least 1), and RIR is how many more clean reps you think you had left (0 or more). The answer is a single estimate in kg to two decimals. Epley is a straight-line approximation, and it also adds a few kilograms to a true single (1 rep, 0 RIR), so it is least reliable at very low and very high rep counts.

Worked example

You lift 100 kg for 5 reps and feel you had 2 reps left. Reps to failure = 5 + 2 = 7. Estimated 1RM = 100 × (1 + 7 / 30) = 100 × 1.2333 = 123.33 kg. Result: estimated 1RM 123.33 kg. If you had stopped at 5 reps with 0 left, the same weight would give 100 × (1 + 5/30) = 116.67 kg.

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Common mistakes

  • Over-rating how close you got to failure, such as calling a grinding set "RIR 3". An RIR guess that is too high makes the estimated 1RM too high.
  • Under-rating RIR because the last rep was slow. A slow rep is not failure, so a set you could have repeated with good form should be counted as spare reps.
  • Entering RIR as the target for the next set rather than for the set you just did. The field describes the completed set.
  • Trusting the result from sets of 12 or more reps. The Epley estimate drifts upward at high reps, so use heavier sets of about 3 to 8 reps when you can.
  • Entering the weight in pounds. The result is labelled in kg, so convert first.

Sources

About this calculator

Reps in reserve (RIR) is a subjective rating of how many more reps you could have performed before technical failure on a given set — an RIR of 2 on a set of 8 means you could have done roughly 10 reps total. Combined with the actual weight and rep count performed, RIR is added to the reps performed to estimate how many reps you could have done to failure, and the Epley formula (1RM = weight × (1 + reps to failure ÷ 30)) turns that into an estimated true one-rep max without ever testing a single all-out lift.

Strength coaches and lifters using autoregulated training programs rely on RIR-based 1RM estimation because it updates automatically as fatigue, sleep and recovery change how a given weight feels day to day — a maxing-out session isn’t required to know approximately where your 1RM currently stands, which matters because true 1RM tests carry injury risk and take a toll on recovery that most training blocks don’t need to pay.

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