How to Estimate Your 1RM: Epley vs Brzycki Formulas (with Worked Examples)

To estimate your 1RM, take a hard set you already did and run it through a formula. The two most common are Epley (weight x (1 + reps / 30)) and Brzycki (weight / (1.0278 - 0.0278 x reps)). Your 1RM, or one-rep max, is the most weight you could lift one time. You almost never need to actually test it. A tough set of 3 to 6 reps and a bit of simple math gets you within a few percent, with none of the risk.

Here's how both formulas work, why they don't quite agree, and the one that's worth your time.

What "estimated 1RM" means (and why not just test it)

Your 1RM is a true one-rep max: load a bar you can lift exactly once, and lift it once. An estimated 1RM (also written E1RM or est-1RM) skips that. It predicts that single from a normal set. Bench 100kg (220 lb) for 5 hard reps and a formula says your max is somewhere around 115kg (253 lb), no scary single required.

Why estimate instead of test? A true single is the riskiest rep in the gym.

• You need a spotter or safety pins. Miss the lift with neither and you're stuck under the bar.
• Form breaks down under a maximal load, and broken form is where people get hurt.
• One all-out single drains your nervous system and tanks the rest of your session.
• If you miss the rep, you learn nothing. No number, no data, just a bruised ego.

A hard set of 5 has none of that downside. Even if the last rep is an ugly grind, you finished it, so you have a real result to work from. And you get a fresh estimate every single workout instead of once every training cycle.

Takeaway: an estimated 1RM is your max, predicted from a set you already survived. Safer, and you get one every session.

The Epley formula

Epley is the one most apps and lifters use. The equation is short:

estimated 1RM = weight x (1 + reps / 30)

Work a real set. You benched 100kg for 5 reps:

• 100 x (1 + 5 / 30) = 100 x 1.1667 = 116.7kg

In pounds, same idea. You benched 225 lb for 5:

• 225 x (1 + 5 / 30) = 225 x 1.1667 = 262.5 lb

Epley leans a little high at moderate reps, a solid pick if you train in the 5 to 8 range. One quirk: at exactly 1 rep it adds about 3 percent (100 x 1.033 = 103kg), so it slightly overshoots a true single.

Takeaway: Epley is weight x (1 + reps / 30). Fast, and it fits the 5 to 8 rep sets most people live in.

The Brzycki formula

Brzycki (say it "bruh-ZINK-ee") takes a different route:

estimated 1RM = weight / (1.0278 - 0.0278 x reps)

Run the exact same set, 100kg for 5:

• 100 / (1.0278 - 0.0278 x 5) = 100 / (1.0278 - 0.139) = 100 / 0.8888 = 112.5kg

In pounds, 225 lb for 5:

• 225 / 0.8888 = 253.2 lb

Notice the gap. On the same 100kg x 5 set, Epley said 116.7kg and Brzycki says 112.5kg, about 4kg apart. Neither is wrong; they just do the math differently.

Brzycki nails a true single exactly (at 1 rep it returns your weight, no bump), so it shines when you're estimating off very low reps, like a heavy triple or a double.

Takeaway: Brzycki reads a touch lower than Epley in the middle rep ranges and is your pick for low-rep sets under 5.

Epley vs Brzycki side by side

Here's the same 100kg lifted for different rep counts through both formulas:

Why do they drift apart? Epley is a straight line: add reps and the estimate climbs at a steady rate. Brzycki is a curve. Its bottom number (the denominator) shrinks as reps go up, and a shrinking bottom makes the whole result balloon. Around 37 reps that bottom number hits zero and the formula breaks completely, spitting out nonsense. The math is telling you not to estimate off a set of 20.

The table shows them meeting near 10 reps, then Brzycki shooting past Epley. Below that, in the 1 to 8 range you actually train in, they sit within about 2 to 4 percent of each other. Close enough that the choice barely matters, as long as you're consistent.

Takeaway: the two formulas agree within a few percent on real working sets and only split apart at high reps, where neither should be trusted.

How accurate are these estimates, really?

Both formulas are at their best between 3 and 6 reps. That's the sweet spot: close to your max, but nowhere near a risky single.

Push past 10 reps and accuracy falls apart. A set of 15 has too much endurance mixed in for the number to mean much, and Brzycki inflates fast. Keep estimates to lower-rep work.

The other rule matters just as much. Estimate from a hard set, not a warm-up. The formulas assume the set was genuinely tough, somewhere around RPE 8 to 9 (that's a rating of perceived exertion, where 10 is nothing left in the tank). If you did 100kg x 5 with four more reps in you, the formula thinks that was near-maximal and hands you a wildly low number. Garbage set in, garbage max out.

Takeaway: estimate from a hard set of 3 to 6 reps near failure. Warm-ups and easy sets lie to the formula.

Which formula should you use?

Short answer: pick one and never switch. The formula you choose matters far less than using the same one every time.

Here's why. If you estimate today's set with Epley and next month's with Brzycki, the number can jump 3 or 4 percent from the math alone, and you'll swear you set a PR (personal record, your best-ever result) that you never earned. You're tracking a trend, and a trend only works if the ruler stays the same.

Can't decide? Two easy defaults:

• Train mostly in the 5 to 8 rep range? Use Epley.
• Live in heavy triples and doubles? Use Brzycki.
• Want a middle number? Average the two. On that 100kg x 5 set, (116.7 + 112.5) / 2 = about 114.6kg.

Takeaway: any of the three works. Just lock it in and stop switching, or you'll fake progress that isn't real.

The real power move: track est-1RM as a trend

One estimated 1RM on its own is just a party trick. The value shows up when you watch it climb.

Think about what that one number captures. Add 2.5kg to the bar? Your est-1RM goes up. Grind out one extra rep at the same weight? It goes up too. It rolls heavier weight and extra reps into a single figure, which makes it the cleanest answer to the only question that matters: am I actually getting stronger?

That beats staring at raw weights, where a rep PR hides because the number on the bar didn't move. For the fuller picture, see how to know if you're making progress in the gym.

The catch is the math. Nobody's running Epley between sets with their forearms on fire. That's the job a tracker should do for you. Ironi works out your estimated 1RM from every logged set automatically, charts the trend so you can see it rise week over week, and flags a PR the second a set beats your best. No calculator, no spreadsheet, and the tracker is free forever. If PRs are new to you, here's what PR means in the gym and the four kinds worth tracking.

Takeaway: log every hard set, let your est-1RM update on its own, and watch the trend. That rising line is your progress.

Quick-reference cheat sheet

Keep this handy:

• Epley: weight x (1 + reps / 30). Best for 5 to 8 reps.
• Brzycki: weight / (1.0278 - 0.0278 x reps). Best for 1 to 5 reps.
• Accurate range: 3 to 6 reps. Trust nothing past 10.
• Use a hard set, RPE 8 to 9, never a warm-up.
• Pick one formula and stay consistent, or average both.
• Watch the trend, not any single number.

Now you can know your max without ever risking one. Pull a hard set from your last workout, run the math once, and start tracking the line.