One rep max calculator

How it works

Reps plus reps in reserve gives the reps you could have done. That number goes through Epley:

• 1RM = weight × (1 + (reps + RIR) / 30)
• RIR above 3 counts as 3, since lifters judge it poorly far from failure (Halperin 2022)
• a single with nothing left is its own 1RM

So 100 kg for 5 with 2 in reserve is 7 reps to failure: 100 × (1 + 7/30) = 123.3 kg. The six other formulas run on the same 7 reps. At 1 rep to failure, all seven return the weight lifted.

Lombardi's exponent is 0.10 in Reynolds 2006 and 0.13 in Mayhew 2008. We use 0.10.

The rep-max table runs Epley backwards from your estimate. Loads round to the nearest 1.25 kg up to 40 kg, 2.5 kg above, or 5 lb.

How far to trust it

Every formula was fitted to sets taken to failure, and each gets less accurate as the reps climb.

• Fewer than 10 reps gave better estimates (Mayhew 2008, 103 women, bench press).
• Reynolds and colleagues advise using no more than 10 reps in a linear equation (Reynolds 2006).
• In that study, a 5 kg error in a 5RM grew to 19.7 kg in the predicted leg press 1RM. On the chest press it was 6.3 kg.
• In 67 untrained students, every equation under-predicted the deadlift (LeSuer 1997).

The reliability grade is ours, set by reps to failure: 1 to 6 high, 7 to 12 moderate, above 12 rough.

No study has tested adding reps in reserve to reps for a 1RM estimate. We do it because Povver does, and because lifters judge RIR near failure to within about one rep (Halperin 2022). Far from failure, the answer is a guess. Read the range.

The range is reps to failure, plus or minus a quarter of itself, run through Epley. Enter RIR and it widens by one more rep. The quarter is how much lifters differ: at a given share of 1RM, the reps people manage vary by about a quarter of the average (Nuzzo 2024). The extra rep is the usual miss in judging RIR (Halperin 2022).