One Rep Max Calculator

By Jack Kyle — Jack Kyle writes about strength training and lifting math — calculators, programming and standards — with a focus on honest numbers and practical guidance.

Key findings

  • Estimates are planning numbers, not measurements — most reliable from hard sets of 1–5 reps.
  • Consensus mode shows six formulas side by side. Read the spread as a reliability signal: a tight spread means a stable estimate, a wide spread means retest with a cleaner set.
  • My Median takes the median of the Epley estimates from two or three of your own sets, so one outlier set pulls the result less.
  • If the estimate and the bar disagree, the bar wins.
Strength tools / 1RM

One-Rep Max Calculator

Estimate your max lift — 4 ways, including a median of your own sets' estimates.

Quick targets — weight lifted

Enter 2–3 recent sets to failure. We take the median of your sets' Epley estimates — no curve is fitted.

6 easy10 max effort

When to use which: use this calculator when you took the set to failure or only know weight × reps; use the standalone RPE calculator when you stopped 1–4 reps short and can rate RPE. The standalone RPE calculator is a separate page; this tool's RPE tab is an in-tool estimate for the same idea.

Estimates only — see our Disclaimer

What this calculator does

You walk into the gym with a plan that calls for 85% of your one rep max — and realise you have never actually tested it. Testing a true max is tiring, takes a full session, and carries more risk than a regular training set. That is the gap this calculator fills. Enter the weight you lifted and the reps you completed, and it estimates what you could lift for a single rep, using several well-known formulas side by side so you can see where they agree and where they differ.

It is built for lifters who programme by percentage: 5/3/1, percentage-based blocks, or any plan that sets loads from a max. It also helps when you switch between rep ranges and want a common reference point, or when you want to check whether a recent set was stronger than it felt. Add up to three sets and My Median shows the median of your sets’ Epley estimates, which smooths out a single unusually good or bad set. Use the result as a planning number, then confirm it with real training. If the estimate and the bar disagree, the bar wins.

How it works

Enter a weight and the reps you completed with it. Consensus mode applies six published formulas:

  • Epley: 1RM = weight × (1 + reps ÷ 30)
  • Brzycki: 1RM = weight × 36 ÷ (37 − reps)
  • Lombardi: 1RM = weight × reps^0.10
  • O’Conner: 1RM = weight × (1 + reps ÷ 40)
  • Mayhew: 1RM = 100 × weight ÷ (52.2 + 41.9 × e^(−0.055 × reps))
  • Lander: 1RM = 100 × weight ÷ (101.3 − 2.67123 × reps)

Each formula makes different assumptions, so they rarely agree exactly. That spread is useful information, not a fault: when the formulas cluster together, the estimate is on firmer ground; when they spread wide, treat the number as rough. Read the spread as a reliability signal. A tight spread — a few kilograms across all six formulas — means the estimate is stable enough to plan from. A wide spread means the input set was noisy: retest with a cleaner, lower-rep set rather than averaging the warning away.

My Median is the median of your sets’ Epley estimates. It models nothing about your personal strength curve — it simply takes the middle Epley value across the sets you entered, so one outlier set pulls the result less.

Calibrate to your own sets (My Median)

Population formulas assume an average lifter. Your own sets carry information about you: how your reps fall off with weight, how your technique holds up, how a given day felt. My Median uses that. Enter two or three sets you actually lifted — the calculator takes the Epley estimate from each set and returns the median. The median is the middle value: with three sets it is the one in the middle; with two sets it is the average of the two. One unusually strong or weak set pulls the median far less than it would pull an average, so a single outlier set cannot hijack the result.

My Median fits no curve and models nothing about your personal strength curve — it is a median of Epley estimates, and it still needs honest inputs: sets done to the same standard, at rep counts where the formulas are reliable. Use it when you have two or three recent sets; use a single-set estimate when you only have one.

Limits to know. Estimates are most reliable from sets of 1–5 reps and get shakier as reps climb past 10. A grinder set, a paused set, and a fast set with the same weight and reps can all mean different things, and no formula can see that. The calculator also cannot account for fatigue, sleep, or how the day felt. For background on why two calculators can disagree, read why 1RM calculators give different answers.

Units. The unit switch changes the label (kg or lb) for new entries. It does NOT convert numbers you have already entered — if you switch units, re-enter your numbers in the new unit.

If you want estimates built from effort ratings instead of reps, RPE-based estimates live on the RPE calculator.

Sources

  • Brzycki, M. (1993). Strength testing: Predicting a one-rep max from reps-to-fatigue. Journal of Physical Education, Recreation & Dance, 64(1), 88–90.
  • Epley, B. (1985). Poundage chart. In Boyd Epley Workout. Lincoln, NE: Body Enterprises.
  • O’Connor, B., Simmons, J., & O’Shea, P. (1989). Weight Training Today. St. Paul, MN: West Publishing, pp. 201–204.
  • LeSuer, D. A., et al. (1997). The accuracy of prediction equations for estimating 1-RM performance in the bench press, squat, and deadlift. Journal of Strength and Conditioning Research, 11(4), 211–213.

Lift-specific calculators

Use the calculator above for any lift. For a version tuned to one lift’s rep behaviour and limits, pick your lift:

Once you have your estimate, the plate calculator works out which plates to load, and the Barloadr homepage lists every calculator in one place.

Frequently asked questions

How accurate is a 1RM estimate?

It is a planning number, not a measurement. From a clean set of 2–5 reps it is usually close enough to set training loads. From a set of 12 or more reps it can be well off, because the formulas were built on low-rep data. Always sanity-check the number against a weight you have actually handled.

Which formula should I use?

Compare them rather than picking one blindly. Epley tends to read higher at moderate reps; Brzycki tends to read lower as reps climb; Lombardi sits between them in many cases. If you log estimates over time, stick with one formula so week-to-week changes mean something. Consensus mode on this page shows all six formulas and the spread between them, so you can see the agreement instead of guessing.

What is My Median?

My Median is the median of your sets’ Epley estimates. Enter two or three sets and it returns the middle value. It models nothing — it does not draw a line or a curve through your data. Its value is simple: the median is less affected by one unusually strong or weak set than an average would be.

Can I use it for any lift?

Yes, for any lift where you can record a weight and reps. The formulas do not know which lift you did, so the same caveats apply everywhere: low-rep sets give firmer estimates, and lifts where technique varies a lot between reps give noisier estimates. For lift-specific notes, use the deadlift, bench press, squat, or overhead press calculator above.

Why do different calculators give different numbers?

Because they use different formulas, different rounding, and different rep ranges. Two calculators can both be “correct” implementations of different formulas and still disagree by several kilograms. That is why this page shows several formulas side by side instead of hiding the spread behind one number.

Do I need to test my true max?

Not to use this tool. A tested max is the only way to know the exact number, but many lifters programme for months off estimates alone. If your programme calls for a true max — for a competition or a testing week — treat the estimate as a guide for what attempt to open with, not as a replacement for the test.

See also