ExRx One Rep Max Calculator (Free Alternative)

If you’ve searched “exrx one rep max,” you’ve almost certainly come across ExRx.net’s well-known one-rep max calculator — one of the oldest and most referenced strength-testing tools on the internet. As a strength coach who has used percentage-based programming for over a decade, I want to walk you through exactly how that style of calculator works, the formula behind it, and how to use the free tool on this page as a fast, equally reliable alternative any time you need a number.

What Is ExRx.net’s One Rep Max Calculator?

ExRx.net is a long-running exercise reference site that has offered fitness professionals free calculators, exercise libraries, and strength standards since 1999. Its one-rep max calculator asks for the weight you lifted and the reps you performed, then returns an estimated 1RM along with a column layout showing various percentages of that result — a format the site says it originally introduced in 2001, and one that has since been widely copied across the fitness industry.

If you’re specifically looking for exrx one rep max results, this page gives you the same category of tool: enter your set, get an estimated max, and see the percentage breakdown instantly, without needing to leave this page.

Which Formula Does ExRx Use?

ExRx.net’s calculator is built on the Brzycki formula:

1RM = Weight × 36 ÷ (37 − Reps)

This is exactly why the calculator on this page defaults to Brzycki as well — so if you’re comparing results against an exrx one rep max lookup, the numbers should line up closely when the same weight and rep count are used.

Why the 1–10 Rep Limit Matters

Reference calculators of this style typically restrict input to somewhere between 1 and 10 reps, and that’s not an arbitrary limit — it’s the range the underlying formula was actually validated against. Push the rep count much higher, and the Brzycki formula in particular starts to produce unreliable, sometimes wildly inflated results, since the denominator (37 − Reps) approaches zero as reps approach 37. This calculator caps input at 15 for the same underlying reason, and I’d still recommend sticking to 10 reps or fewer for the tightest possible estimate.

Using This Calculator as an ExRx One Rep Max Alternative

This tool isn’t affiliated with ExRx.net, but it’s built to serve the exact same purpose for anyone searching exrx one rep max: a fast, no-login, percentage-column calculator you can use on any device. The advantage here is flexibility — you can switch between Brzycki, Epley, Lombardi, Mayhew, or an average of all four with a single click, rather than being limited to one formula.

Understanding the Formulas Behind Any 1RM Calculator

Whether you use ExRx’s tool, this one, or any other, nearly every reputable one rep max calculator is built on one of these four validated formulas:

1. Brzycki Formula

1RM = Weight × 36 ÷ (37 − Reps) — the formula ExRx.net uses, well-suited to the 1–10 rep range.

2. Epley Formula

1RM = Weight × (1 + Reps ÷ 30) — the most widely used formula across gym apps generally, slightly more generous at higher reps.

3. Lombardi Formula

1RM = Weight × Reps^0.10 — an exponential model useful as a cross-check.

4. Mayhew Formula

1RM = Weight × 100 ÷ (52.2 + 41.9 × e^(−0.055 × Reps)) — derived specifically from bench press data.

How to Use This Calculator

1. Choose your exercise from the dropdown.
2. Select your unit, kilograms or pounds.
3. Enter the weight you lifted in a recent, clean working set.
4. Enter your reps, ideally 10 or fewer to match the validated range of most reference formulas.
5. Pick Brzycki to mirror an exrx one rep max style result, or choose the average for a more balanced estimate.
6. Click “Calculate My One Rep Max.” You’ll see your estimated 1RM and full percentage chart instantly.

Worked Example

Percentage Chart Explained

Once you have an estimated 1RM, the percentage columns tell you what to lift for different training goals — the same core concept ExRx popularized in its layout back in 2001.

Brzycki vs. Epley: Which Should You Trust?

Neither formula is objectively “more correct” — they’re both validated regression models built from real lifter data, just with slightly different assumptions. When precision really matters, I tell clients to check both and treat the average as their working number, which is exactly what this calculator’s “Average of All Formulas” option does automatically.

How Accurate Are These Estimates?

Both Brzycki and Epley-based estimates typically land within 2–5% of a genuinely tested 1RM when the input set was performed with clean technique, in the 1–10 rep range, and wasn’t taken to complete failure. Accuracy drops noticeably outside that range regardless of which formula or which reference calculator you use.

Common Mistakes to Avoid

1. Entering more than 10 reps and expecting reference-formula accuracy — both Brzycki and most classic calculators were validated well below that.
2. Using a failure set. A grinding final rep skews any formula, including Brzycki.
3. Comparing numbers across formulas without context. A few kg of difference between Brzycki and Epley results is normal, not an error.
4. Treating the estimate as a fixed ceiling. It’s a planning tool, not a permanent limit — recalculate as you get stronger.

Want a second opinion on your number? The general one rep max calculator is a handy companion tool for cross-checking results across formulas and devices.

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And for the days a heavy top set feels daunting, a little motivation goes a long way — besturduquotes.net is a nice source of short, motivating lines to read before you chalk up.

Frequently Asked Questions About ExRx One Rep Max

Final Thoughts on ExRx One Rep Max Calculators

Reference calculators built on the Brzycki formula, like the one popularized by ExRx.net, have earned their reputation for a reason — they’re simple, validated, and easy to apply within the 1–10 rep range they were designed for. This page gives you that same style of estimate, with the flexibility to cross-check it against Epley, Lombardi, and Mayhew whenever you want a second opinion. Use an honest, clean input set, stick to 10 reps or fewer for the tightest accuracy, and let the percentage chart guide your next training block.