One rep max calculator: estimate your 1RM from weight lifted and reps using Epley, Brzycki, and Lombardi formulas with training charts. Free, no signup.
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Every figure above is calculated locally in your browser from the assumptions shown. No inputs are sent anywhere. See the methodology section below for the formulas used.
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One rep max calculator: estimate your 1RM from weight lifted and reps using Epley, Brzycki, and Lombardi formulas with training charts. Free, no signup.
At 15 reps the Epley and Brzycki estimates split by 30 lb.
Transparent methodology
How this calculator works
Reviewed August 2026 · BoringToolsKit Editorial Team
BoringToolsKit. “One Rep Max Calculator.” boringtoolskit.com/one-rep-max-calculator/ (reviewed August 2026). Free to reference in articles, syllabi, and answer posts with a link.
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Worked example: 135 lb for 5 reps
Take a lifter who grinds out 135 lb for 5 clean reps on bench. The Epley formula multiplies the weight by (1 + reps/30), so the first step is 5/30 = 0.1667, giving a multiplier of 1.1667. Then 135 x 1.1667 = 157.5, which rounds to an estimated one-rep max of 158 lb.
The reverse check confirms the internal logic: 100 / 1.1667 = 85.7, so a 5-rep set runs at about 86% of true max. That matches the published Epley load table, which places 5 reps in the 85 to 87% range. Plugging the same numbers into the calculator should return 158 lb and an 86% figure. Note the rounding: the raw estimate is 157.5 lb, and programming 158 on a bar means loading a 45, a 35, and two 2.5 lb plates per side minus 45 per side, or simply using 155 or 160 for round-plate math.
Watch what happens with a longer set. The same lifter doing 135 lb for 12 reps gets 135 x 1.4 = 189 lb estimated, a 31 lb jump from six extra reps. That nonlinearity is why sub-10-rep sets give the most trustworthy estimates.
Where the estimate breaks down
Epley was fit on relatively low-rep lifting data, and the error grows as reps climb. At 10 reps of 225 lb, Epley predicts 300 lb. The Brzycki formula (weight x 36 / (37 - reps)) predicts 219.7 x 36/27... more simply 225 x 36/27 = 300 lb here, but at 15 reps the two split: Epley gives 225 x 1.5 = 338 lb while Brzycki gives 225 x 36/22 = 368 lb, a 30 lb spread. Past about 12 reps neither formula deserves much trust; treat anything above that as a rough ceiling, not a programming target.
Form also shifts the answer. A paused bench or deep squat rep is harder than a touch-and-go rep, so high-rep bounce sets overstate the max. Speed matters too: if the last rep took 6 seconds to lock out, the set was closer to failure than the rep count implies, which pushes the real max lower than the estimate. Lifters on creatine or in a caloric surplus can also swing 5 to 10 lb week to week, so retest the estimate every 4 to 6 weeks rather than anchoring to a single session. Finally, never jump straight to the computed 1RM in training; most coaches program at 85 to 95% of the estimate for singles, which for a 158 lb max means working between 134 and 150 lb.
