One Rep Max Calculator

What a one rep max actually is

Your one rep max, or 1RM, is the heaviest weight you could lift for a single clean rep on a given lift. Testing it directly means loading the bar until you fail, which is fatiguing, eats into your training week, and carries real injury risk if your form breaks down under a true max attempt. Estimating it from a set you have already done well gets you a number that is close enough to plan around, without any of that risk. That is what the calculator above does.

The formula behind the estimate

This calculator runs the Brzycki formula: weight times 36, divided by (37 minus reps). The idea is that each additional rep at a given weight represents a predictable slice of your true max. You will also see Epley elsewhere, weight times (1 plus reps divided by 30), which models that slice slightly differently. The two agree almost exactly around 10 reps but drift apart at lower rep counts, where Epley reads several pounds higher, and neither style of estimate should be trusted much beyond 12 to 15 reps, since fatigue stops behaving in a straight line that far out.

A worked example

Say you squat 225 pounds for a clean set of 5 reps. Brzycki, the formula this tool uses, puts that at 225 times 36, divided by 32, which comes out to about 253 pounds. Epley would call the same set 225 times 1.167, landing at roughly 262 pounds, about 9 pounds higher. Either way the message is the same, your true single is somewhere in that neighborhood, not a value to treat as exact to the pound.

Working percentages

• About 95%: a heavy single or double
• About 85%: a solid set of 5
• About 70 to 75%: hypertrophy work in the 8 to 12 rep range

Those bands are the practical use for your estimated 1RM, picking working weights for a given rep target without guessing. Keep in mind the estimate itself gets less reliable the higher the rep count you plug in to generate it. A 1RM estimated from a set of 3 is on firmer ground than one estimated from a set of 15.

What to do with your number

Use your estimated 1RM to set training loads, not as a score to chase. Pair it with your RPE and percentage calculator to pick a weight for a target rep and effort, your training max to build a program around a slightly conservative number, and your warmup calculator to build up to your working sets without wasting energy. If you want the estimate explained from the top, without the formulas, how to calculate your one-rep max walks it through in plain terms. Retest every few weeks as you get stronger and let the number move with you.