One-Rep Max Calculator
Estimate your true 1RM from any rep-max set with the Epley formula. Free strength calculator plus a full 50–95 percent training-load table for programming.
The one-rep max (1RM) is the gold-standard reference for strength training. It is the heaviest weight you can lift for a single, technically clean repetition of a given lift, and almost every modern training program — from 5/3/1 to Sheiko to RP — prescribes load as a percentage of it.
Testing a true 1RM is unnecessary for most lifters and carries some injury risk. The Epley formula gives a reliable estimate from any set in the 1–10 rep range, so you can plug in your last hard top set and pull back a working 1RM for programming purposes. This calculator uses Epley because it is the most widely validated formula and the same one the MuscleBuddy training engine uses internally for percentage-based progression.
Enter the weight you lifted and the number of clean reps you completed — ideally a set taken to one or two reps shy of failure. The result is your estimated 1RM plus a percentage table covering the load ranges you will actually program around.
Training-load table
How this works
The Epley formula is 1RM = weight × (1 + reps / 30). It was published by Boyd Epley in 1985 in the National Strength & Conditioning Association journal and is one of three formulas (alongside Brzycki and Lander) that dominate the modern literature. Epley assumes a roughly linear drop in completable reps as load approaches your true maximum — about a 3.3% intensity drop per additional rep.
For a 100 kg × 5 set, Epley estimates a 1RM of 100 × (1 + 5/30) = 116.7 kg. For a 100 kg × 3 set, the estimate drops to 110 kg, which lines up with the reality that closer-to-max sets are more honest indicators of true strength. The formula starts to drift above 10 reps because muscular endurance and pacing begin to dominate raw force production.
For the most accurate estimate, use a set taken to one or two reps in reserve (RIR) — not a grinding set to failure and not a comfortable set with reps left in the tank. Sets where you barely finished the last rep tend to overstate your 1RM; conservative sets understate it.
Once you have your 1RM, the percentage table below shows the working weights for common intensity zones: 90–95% for singles and doubles (peaking), 80–85% for triples and 4s (strength), 70–80% for 5–8 rep work (hypertrophy + strength), and 60–70% for higher-rep accessory and volume work. Round to the nearest plate-compatible increment — 2.5 kg or 5 lb — so the load is actually loadable on a standard barbell.
Frequently asked questions
- What is a one-rep max (1RM)?
- Your one-rep max is the heaviest load you can lift for a single, full-range repetition of a given exercise. It is the standard reference point used to prescribe training percentages.
- How accurate is the Epley 1RM formula?
- Epley is accurate within about 5% for sets in the 1–10 rep range. Accuracy degrades sharply above 10 reps because muscular endurance starts to outweigh maximal strength.
- How many reps should I use for the most accurate estimate?
- Sets of 3 to 5 reps taken to one or two reps shy of failure give the cleanest estimate. Singles only give you exactly what you lifted; high-rep sets overstate your true 1RM.
- Should I test my actual 1RM or use a calculator?
- For most lifters, an estimated 1RM is safer and just as useful. Reserve true 1RM tests for powerlifters in the final weeks of a peaking block — they carry real injury risk.
- Can I use this for any lift?
- Yes. The Epley formula is exercise-agnostic — it works for squats, benches, deadlifts, presses, and rows. Isolation exercises with very short ranges of motion (curls, lateral raises) are less reliable.
- How often should I update my 1RM?
- Every 4–8 weeks, or after any block where you set a new top set. Training percentages drift out of date fast if your strength is climbing.
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