The weight for your next set matters more than your max
Your one rep max (1RM) is the most you could lift once. Unless you compete, you'll rarely lift it. The weights in the table are the ones you'll actually pick up. The US activity guidelines say one set of 8 to 12 reps of each exercise is effective, taken to the point where another rep would be hard.
Take the set the calculator opens with: 8 reps at 20 lb. That's a max of about 25 lb. What you'd actually grab: 20 lb for 8 reps, 15 lb for 12.
Treat the 10 and 12 rep rows as a first guess. They're the least sure. Then let the set tell you. If you finish 12 and could keep going, take the next dumbbell. If you can't reach 8, go down one.
Did you stop your set a few reps before you couldn't do another? That's fine. The American College of Sports Medicine says stopping a few reps short of failure is enough to get stronger. Your estimate will just come out a little low. You had more reps in you than you typed, and low is the better way to be wrong.
Between two dumbbells? Take the lighter one
The math rarely lands on a dumbbell you own. The table rounds down to the step you pick: 5 lb or 2.5 lb, 2.5 kg or 1 kg. A last rep that's hard beats one you can't finish.
With the lighter dumbbell, add reps each session until you reach 12. Then move up a dumbbell and start back near 8. Come back and run the calculator again with your new set.
Annie, a novice at weights with only a few items at home, wrote in a Solin review that "when I need bigger weights that will be an occasion to celebrate!" That occasion comes the day you hit 12 reps with the dumbbell you used to do 8 with.
Sets under 10 reps give the best 1RM estimate
The calculator runs two standard formulas and shows you both.
- Epley: 1RM = weight × (1 + reps ÷ 30)
- Brzycki: 1RM = weight ÷ (1.0278 − 0.0278 × reps)
Your estimated max is the average of the two. For the table, each formula runs in reverse: from its own max, it gives the weight for 5, 6, 8, 10 and 12 reps. Those two answers are averaged too.
Neither formula started as a study. A 2026 paper by Fitbod's Thiago Marzagao traces Epley to a training manual's chart and Brzycki to a 1993 article for coaches. The same paper sums up the studies that tested them. One followed 103 women before and after 12 weeks of training and found the formulas did better with sets of fewer than 10 reps to failure. Another, in 70 men and women aged 18 to 69, found a 5-rep set predicted the max best.
Two more limits. People differ: in a 2023 analysis of many studies, at 80% of their max the typical spread between people was about 2.5 reps. And the leg press allows more reps than the bench press at the same share of your max: 13.1 reps at 80%, against 8.8. Lower-body moves often show bigger errors than the bench press, so a squat estimate can be further off than a press estimate.
Skip the max test if you lift alone
A real max test takes several build-up sets with 2 to 4 minutes of rest between attempts. Human Performance Resources, a US military health site, says a test with more reps is a good option if you're lifting by yourself and don't have someone to spot you. A spotter is a person who stands by to help if you get stuck. This calculator needs none. It works from a set you've done before.
New to lifting? Start low and go slow. Our guide to strength training for beginners shows how to pick your first weights, and the 6-week workout plan gives you the moves and sets week by week. If you have a health condition, ask your doctor what's right for you. Pregnant or had a baby recently? Check with your doctor first.
Lift with a group
Of 93 challenge winners we interviewed, 90% credited the challenge community for motivation and support. A Solin challenge gives you the plan, a start date and that group, with a 30-day money-back guarantee. Lift together, not alone.
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