How to Calculate Your One-Rep Max

Your one-rep max (1RM) is the heaviest load you could lift once for a given exercise with solid technique. You rarely need to test it under a true maximal single. For most gym programming, a formula estimate from a hard submaximal set is safer and repeatable enough.

This guide walks through the two formulas used on our One-Rep Max Calculator — Epley and Brzycki — and how to use the result with plate loading and RPE.

Why estimate instead of testing a true max

A true 1RM attempt needs a long warm-up, fresh recovery, and a readiness to miss. Estimates are useful when you want:

• Working weights as a percentage of 1RM
• Progress checks without peaking every cycle
• A shared reference for programs written in %1RM

Treat every estimate as a training number, not a competition total. Formulas are population averages; individual day-to-day strength varies.

Step 1: Choose a clean submaximal set

1. Warm up with light ramping sets on the same lift.
2. Pick a weight you can lift for about 3–8 reps with the same technique you use in training.
3. Stop near failure — roughly 0–1 reps left — while keeping form intact. If technique breaks, stop the set and use the last clean rep count.
4. Record weight, reps completed, and the exercise (for example bench press, squat, or deadlift).

Sets much longer than about 10–12 reps are a poor fit for 1RM formulas. At that point muscular endurance starts to dominate the result.

Step 2: Apply Epley and Brzycki

With weight w and reps r (where r is greater than 1):

• Epley: 1RM = w × (1 + r / 30)
• Brzycki: 1RM = w × (36 / (37 − r))

If you completed a true single (r = 1), the estimate is simply the weight lifted.

Worked example

You squat 100 kg for 5 clean reps near failure.

Our calculator shows all three so you can see the spread. When they disagree by more than a small margin, re-check that the set was actually close to failure and within the 2–10 rep range.

Step 3: Round to a loadable weight

Round the estimate to the nearest plate jump you can load — often 2.5 kg or 5 lb. False precision (for example 231.4 lb) does not make the estimate more accurate.

Use the Plate Loading Calculator to convert a target barbell weight into plates per side for kg or lb inventories.

Step 4: Turn 1RM into training loads

Common starting zones (approximate):

These are starting points, not prescriptions. How many reps you can do at a given percentage also depends on the lift, fatigue, and how the set feels.

Using RPE when the set was not quite to failure

If you stopped with reps in reserve, a percentage chart based on reps × RPE can be a better bridge than pretending the set was a max-effort set. Our RPE & Rest Calculator maps common reps × RPE combinations to an approximate %1RM, and can estimate an e1RM or a target load from a known 1RM.

A simple RIR helper used there is RIR ≈ 10 − RPE (for example RPE 8 ≈ 2 reps in reserve). For choosing working-set loads and mid-session adjustments, see How to Use RPE for Working Sets.

Limitations to keep in mind

• Formulas drift as reps climb past roughly 10–12.
• Machines, isolation lifts, and very slow tempos may not match free-weight research averages.
• Poor sleep, stress, or a hard training week can move your “true” max without the formula knowing.
• Never chase a formula number through broken technique.

Put it to work on real lifts

Estimate 1RM on the lifts you actually train, then open the matching exercise guide for setup and range-of-motion cues:

• Bench Press
• Full Squat
• Deadlift

When your working sets get easier at the same RPE, re-run the estimate and update your percentages.

Quick links

• One-Rep Max Calculator — Epley, Brzycki, and training percentages
• RPE & Rest Calculator — reps × RPE → %1RM and rest ranges
• Plate Loading Calculator — load the bar to your target
• All fitness calculators
• Exercise library