5×5 One Rep Max Calculator

Estimate your one-rep max from a StrongLifts 5×5 working weight. A 5×5 weight is submaximal, so an ordinary 1RM calculator under-reads your real max. This one corrects for set fatigue based on how hard your last set felt, then gives you %-of-max and rep-max tables and the exact loads for your next session, with the plates to put on each side of the bar.

Lift

How did you lift it?

5×5 working weight

the weight you put on the bar for all 5 sets of 5

Last-set effort

Grippy — 1–2 reps left on the last set

Enter your 5×5 working weight. Your estimated 1-rep max appears here.

5RM vs 5×5: why generic calculators get this wrong

Standard 1RM calculators assume the reps you enter were one all-out set, a true rep-max. A StrongLifts or Bill Starr 5×5 working weight is not a 5-rep max: you do five sets, so you deliberately leave reps in reserve to finish them all. Feed that submaximal weight into a plain calculator and it underestimates your true 1RM.

The fix is to back out the fatigue. A true 5RM is roughly 86–89% of your 1RM, while a 5×5 weight sits lower, around 78–85%, depending on how hard the last set was. This calculator applies the right correction from the effort you pick, instead of pretending your 5×5 weight was a max set.

How to estimate 1RM from a 5×5

Multiply your 5×5 working weight by a factor set by last-set effort:

Last set felt…	× factor	≈ % of 1RM	Basis
Grind (near failure)	×1.15	~87%	≈ a true 5RM
Hard (1–2 left)	×1.20	~83%	Faleev's rule
Moderate (~3 left)	×1.25	~80%	—
Easy (plenty left)	×1.28	~78%	Texas-method chain

Worked example: you squat 100 kg for 5×5 and the last set was hard. Estimated 1RM ≈ 100 × 1.20 = 120 kg. A generic calculator, treating it as a 5-rep max, would say only ~117 kg, and far less if you'd taken it easy.

The 1RM formulas (for one all-out set)

Switch to One all-out set mode and the calculator uses the established rep-max formulas, showing the spread rather than one false-precise number. With weight w and r reps:

Epley: w × (1 + r/30)
Brzycki: w × 36 / (37 − r)
Lombardi: w × r^0.10
O'Conner: w × (1 + r/40)

All of them lose accuracy above ~10 reps, so base your estimate on as few reps as you can.

How to use this calculator

Pick your lift and choose kg or lb.
Keep StrongLifts 5×5 mode and enter the weight you use for all five sets.
Tap how hard the last set was; that sets the fatigue correction.
Read your estimated 1RM range, then use the %-of-max and rep-max tables, or open Plan my next session for your working loads.

Frequently Asked Questions

What is a 5×5 one rep max calculator?

It estimates your one-rep max (1RM) from the weight you lift for 5 sets of 5 (5×5), the way StrongLifts and Bill Starr programs are run. Unlike a generic 1RM calculator, it accounts for the fact that a 5×5 working weight is submaximal (you hold back to finish all five sets), so it doesn't under-read your true max.

Why isn't my 5×5 weight the same as a 5-rep max?

A true 5-rep max (5RM) is one all-out set where the fifth rep is the most you could do. In 5×5 you do five sets, so you deliberately use a lighter, submaximal weight to survive the volume. A true 5RM is about 86–89% of your 1RM; a 5×5 working weight is usually nearer 78–85%, depending on how hard the last set is. That's why plugging a 5×5 weight into an ordinary 1RM calculator underestimates your max.

How do I estimate my 1RM from 5×5?

Take your 5×5 working weight and multiply it by roughly 1.15–1.30 depending on last-set effort: about ×1.15 if the last set was a near-failure grind, ×1.2 if hard (Faleev's rule), up to ×1.27 (the Texas-method chain) if it still felt comfortable. This calculator picks the right multiplier from the effort you select and shows the result as an honest range.

Which 1RM formula is most accurate?

For one all-out set, Epley and Brzycki are the most widely used and agree closely at low reps; we show Epley, Brzycki, Lombardi and O'Conner side by side so you see the spread. All estimating formulas get less accurate above about 10 reps, so the fewer reps you base the estimate on, the better.

How often should I test my actual 1RM?

Most lifters only need a true 1RM test every few months, or before a meet, since maxing out is fatiguing and carries more injury risk than estimating. Use this calculator week to week, and verify with a real attempt occasionally.

Is my data sent anywhere?

No. The calculator runs entirely in your browser. Nothing you type is stored or sent to a server.