One Rep Max Calculator Widget

Add a one-rep max calculator to your website. Lifters enter the weight and the reps they completed and see their estimated one-rep max by the Epley and Brzycki equations, the average of the two and a table of training loads from 100% down to 50%.

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<iframe src="https://a2z.tools/embed/w/one-rep-max-calculator" title="One Rep Max Calculator by A2Z Tools" width="100%" height="760" style="border:0;width:100%" loading="lazy" allow="clipboard-write"></iframe>

A plain iframe. Works everywhere, including site builders that strip scripts. Adjust height if your content needs more room.

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How it works

Epley (1985) and Brzycki (1993) are the two most widely used 1RM equations, and the same pair appears on the A2Z One Rep Max Calculator. They agree closely at low reps and drift apart as reps rise, so the widget shows both, their difference and their average. The loads table applies percentages to the average, and the typical-reps column is the Epley equation solved for repetitions, which lines up with standard strength-training percentage charts (about 8 reps at 80%). Sets are limited to 12 reps because the equations were validated on low-rep sets - LeSuer and colleagues found prediction accurate up to about 10 repetitions - and above 10 reps a note suggests testing with a heavier set.

Calculation method

  • Epley: 1RM = weight x (1 + reps / 30); a single rep returns the weight itself
  • Brzycki: 1RM = weight x 36 / (37 - reps)
  • Estimate shown = (Epley + Brzycki) / 2, to 1 decimal place in kg or lb
  • Load at p% = estimate x p / 100; typical reps at p% = 30 x (100 / p - 1), rounded

Worked examples

Five-rep set

Inputs: 100 kg x 5 reps

Result: Estimated 1RM 114.6 kg (Epley 116.7, Brzycki 112.5); 80% load 91.7 kg for about 8 reps

100 x (1 + 5/30) = 116.67; 100 x 36 / 32 = 112.5.

An estimate for general information only. Lift heavy loads with proper technique, a warm-up and a spotter or safety equipment.

Limitations

  • Accuracy depends on the set being taken to genuine failure with good form; stopping short underestimates the 1RM.
  • Validation studies found all equations underestimate the deadlift, and they fit trained and untrained lifters differently.
  • Sets of more than 12 reps are refused.

Where publishers use it

  • Strength coaches and powerlifting clubs writing percentage-based programmes
  • Gym websites with a member tools page
  • Fitness bloggers explaining progressive overload
  • CrossFit and weightlifting box sites where members track lifts

Questions

Is it safe to test a true one-rep max?

It can be done safely with good technique, a proper warm-up and a spotter or safety bars, but many lifters prefer to estimate it from a heavier set of 3 to 6 reps, which is what this widget does.

Why are Epley and Brzycki different?

They are separate curve fits to lifting data. They give the same answer at ten reps (both 1.333 x the weight) and diverge slightly below and more beyond ten.

Why is the limit 12 reps?

The equations were fitted to low-rep sets, and validation work such as LeSuer's 1997 study found them accurate up to about ten repetitions. Past that the error grows quickly, so higher-rep sets are not accepted.

Can it show pounds?

Yes. Switch to Imperial, or add units=imperial to the embed URL.

Sources

  1. Strength testing - predicting a one-rep max from reps-to-fatigue (Brzycki) - Journal of Physical Education, Recreation & Dance 64(1):88-90, 1993 . Brzycki equation
  2. Poundage chart (Epley) - Boyd Epley Workout, Lincoln, Nebraska, 1985 . Epley equation (print source)
  3. The accuracy of prediction equations for estimating 1-RM performance in the bench press, squat, and deadlift (LeSuer et al.) - Journal of Strength and Conditioning Research 11(4):211-213, 1997 . Validation of seven equations up to 10 reps

Cite or recommend this tool

If you reference this tool in an article, course or documentation, these formats are ready to copy. They are optional - nothing is added to your site unless you paste it.

A2Z Tools One Rep Max Calculator
https://a2z.tools/one-rep-max-calculator

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