One rep max calculator

How the estimate works

Testing a true one rep max takes a long warm-up, a heavy single and some risk. A calculator skips that. It takes a set you already did and predicts the heaviest single you could manage on the same day. This page uses the two formulas most calculators are built on and shows both.

A worked example. You bench 225 lb for 5 reps. Epley gives 225 × (1 + 5 ÷ 30) = 262.5 lb. Brzycki gives 225 × 36 ÷ 32 = 253.1 lb. The average of the two is 257.8 lb, and that is the number the percentage table uses.

The two formulas give the same answer at 1 rep and at 10 reps. Between 2 and 9 reps Epley reads higher, and above 10 reps Brzycki does. At one rep the result is simply the weight you lifted, because a single needs no prediction.

When not to trust the number

Every estimate assumes the set was a real effort. It gets worse in a few common cases:

• The set had more than 10 reps. Past that point endurance matters more than strength, and the two formulas start to disagree. The calculator warns you above 10 reps and stops at 12.
• The set was not close to failure. If you could have done three more reps, the estimate comes out too low.
• The lift is a machine, a cable or a small isolation movement. The formulas are most at home on barbell lifts like the squat, bench press and deadlift, so treat other numbers as rougher.
• You are not an average lifter. Some people can do many reps at a high percentage of their max and some can do very few, and a formula cannot tell which one you are.

None of this makes the number useless. Use it to plan training, not as a target you must hit on the day.

How to use percentages to pick working weights

Most strength programs write sets as a percentage of your 1RM, such as 5 sets of 5 at 80%. The table in the calculator does that multiplication for you and rounds to a weight you can load with standard plates: 2.5 kg steps or 5 lb steps.

If your program does not give percentages, run the formulas backwards. They put 85% of your max at about 5 to 6 reps to failure, 80% at about 7 to 8, and 75% at about 10. For sets you want to finish with a rep or two left in the tank, pick one step lower than the percentage that matches your reps to failure.

Re-estimate every few weeks from a recent hard set. A max from three months ago will set every percentage too light if you have been getting stronger, or too heavy if you have had time off.

How SayLift sets your next working weight

A percentage chart gives you a starting weight. It does not tell you what to do next session after a good day or a bad one. That is the question the coach in SayLift answers.

SayLift is an iPhone workout tracker you log by talking. Its coach reads your own logged history and, for each exercise, gives you one instruction: increase, hold, decrease, deload, restart, calibrate. That instruction comes with the working weight for your next session, so you do not need to redo the maths between sets.