One Rep Max Conversion Calculator

“Conversion” is one of the most useful but least explained concepts in strength training. Most lifters think of a one rep max as a single, fixed number, but in practice you’ll constantly need to convert it — into a working weight for a different rep range, into an estimate from a set you didn’t intend as a max test, or simply from kilograms into pounds when your gym’s plates use a different unit than your log. After more than a decade coaching lifters through exactly this kind of practical math, I built this guide — and the calculator above — around the three conversions I get asked about most.

What Is One Rep Max Conversion?

One rep max conversion is the process of translating a known or estimated 1RM into a different, more immediately useful number — usually a target training weight for a specific rep range, or the reverse: turning a submaximal set into an estimated 1RM in the first place. It also commonly refers to converting weight values between kilograms and pounds, which matters constantly for lifters who train across gyms using different plate systems or follow programs written in a different unit than they’re used to.

Three Types of One Rep Max Conversion

When people search “one rep max conversion,” they’re usually looking for one of these three things, all of which are built into the calculator above:

• 1RM → target reps: You know your max and want to find your working weight for, say, a set of 8.
• Set → 1RM: You have a submaximal set and want to convert it into an estimated 1RM (the reverse direction).
• kg ↔ lb: You need to convert a weight value between metric and imperial units, often to match a program or a gym’s plates.

Converting 1RM to a Target Rep Range

If you already know your 1RM, converting it to a target rep range simply means solving the same formulas in reverse. For the Epley formula:

Target Weight = 1RM ÷ (1 + Reps ÷ 30)

For Brzycki:

Target Weight = 1RM × (37 − Reps) ÷ 36

This is exactly what the “1RM → Target Reps” tab in the calculator above does automatically — enter your known max and a target rep count, and it converts it into the weight you should load for that many reps.

Converting a Working Set Into an Estimated 1RM

This is the reverse direction, and it’s the more familiar version of a “1RM calculator” — you take a completed set and convert it forward into an estimated max using the standard formulas (Epley, Brzycki, Lombardi, Mayhew). The “Set → 1RM” tab handles this conversion for you.

Converting Between Kilograms and Pounds

The third type of conversion has nothing to do with formulas and everything to do with simple unit math:

Pounds = Kilograms × 2.20462

Kilograms = Pounds ÷ 2.20462

This matters more than people expect. A program written in pounds by a US-based coach needs converting for a lifter training on a metric-only gym’s plates, and small rounding errors compound over a multi-week block if you’re not careful. The kg ↔ lb tab above handles this instantly in both directions.

How to Use the Conversion Calculator

1. Pick the right tab for what you’re converting — 1RM to a target rep range, a set to an estimated 1RM, or kg to lb.
2. Enter your known values — your max, your set, or your weight to convert.
3. Choose a formula if applicable, or leave it on the recommended average.
4. Click “Convert Now.” You’ll get your converted number instantly, plus a full rep-range conversion table where relevant.

Worked Example: Full Conversion Walkthrough

One Rep Max Conversion Table

This table shows how a 100 kg one rep max converts across common target rep ranges, using the Epley formula:

The calculator above generates this same style of table dynamically for your own numbers.

How Accurate Is One Rep Max Conversion?

Rep-range conversions are typically accurate within a few percent when converting to nearby rep ranges (say, 1RM to a 3–8 rep target) and become progressively less reliable the further you convert from a rep range the formula was validated against — generally beyond 12–15 reps. Unit conversion between kg and lb is a fixed mathematical constant and carries no estimation error at all.

Common Conversion Mistakes

1. Converting too far from the original rep range. A 1RM converted to a 20-rep target loses meaningful accuracy.
2. Mixing units mid-calculation. Convert to a single unit first, then run your formula — don’t mix kg and lb in the same equation.
3. Rounding too early. Round only at the final step of a chained conversion (1RM → target reps → unit conversion).
4. Assuming perfect accuracy. Formula-based conversions are estimates; unit conversions are exact, but don’t confuse the two.

Practical Uses for Conversion in Programming

Beyond curiosity, one rep max conversion has real programming value. Coaches use 1RM-to-target-rep conversion to write out an entire training block’s working weights in advance, without needing to test every rep range individually. Athletes traveling between gyms with different plate systems use kg/lb conversion to keep their program consistent regardless of which unit the local plates are marked in. And anyone cross-checking a submaximal set against their known max uses set-to-1RM conversion as a quick sanity check on whether their strength is trending up, flat, or down.

Want a second opinion on a converted number? The general one rep max calculator is a handy companion tool for cross-checking results.

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Frequently Asked Questions About One Rep Max Conversion

Final Thoughts on One Rep Max Conversion

Whether you’re converting your max into a working weight for a specific rep range, converting a submaximal set into an estimated 1RM, or simply converting between kilograms and pounds, the underlying goal is the same: turning one useful number into another useful number without guesswork. Use the calculator above for whichever direction you need, keep your input data clean and honest, and let the conversion do the arithmetic so you can focus on the actual lifting.