Calculator
One rep max calculator
Enter one hard set and get an estimate of your one-rep max, plus the weights that estimate points to for sets of 5, 8, 10 and 12. No max-out attempt needed.
1RM calculator
Enter one hard set
Estimated one-rep max
186.7 lb
| Reps | Weight |
|---|---|
| 5 | 160 lb |
| 8 | 145 lb |
| 10 | 140 lb |
| 12 | 135 lb |
Training for 6–10 reps? Start around 145 lb. ThreeByEight takes it from there: next session’s target, worked out from your last top set, with the reason.
iPhone app coming
What a one-rep max is
Your one-rep max (1RM) is the most weight you can lift once, with good form, on a given lift. It is a handy single number for how strong you are on that lift, and a lot of programs are written as percentages of it.
Testing it directly means working up to a true maximum single. That is tiring, needs a spotter or safety pins on most lifts, and the answer changes as you get stronger. An estimate from a normal hard set gets you most of the value without any of that.
How the estimate works
This calculator uses the Epley formula: your weight, times one plus your reps divided by 30. A set of 10 at 140 lb estimates a 1RM of about 186.7 lb (140 × 1.333).
Most sets don’t go to failure, so the calculator also takes reps in reserve: how many more clean reps you could have done. It counts those as reps you could have lifted, so 8 reps with 2 in reserve is treated like a set of 10. Leave it blank if the set went to failure.
The working-weight table runs the same formula backwards: for each rep count, the weight whose estimate matches yours. Those weights are for a hard set of that many reps, with nothing left in reserve, and they are rounded to the nearest 5 lb.
Getting a good estimate
The estimate is only as good as the set you give it. A few things make it better:
- Use a recent set, not one from months ago.
- Use a hard set: close to failure, or with an honest count of the reps you had left.
- Use clean, full-range reps. Paused, partial or bounced reps skew the number.
- Fewer reps estimate better. A set of 3 to 8 works well.
- Estimate each lift on its own. A bench press max says nothing about your squat.
Why high-rep estimates are less reliable
The further a set is from a single, the more the estimate depends on things a formula can’t see: conditioning, how well you grind out the last reps, the lift itself. A set of 3 says a lot about your max; a set of 20 says more about your endurance.
So the calculator caps reps plus reps in reserve at 12. Anything past that is counted as 12, and the result says so when it happens. The table stops at 12 reps for the same reason. ThreeByEight uses the same formula and the same cap in the app.
Using it to pick a starting weight
A 1RM is most useful as a starting point. If you are beginning a lift in a rep range, start a little under the weight you could do for the top of your reps, so the first sessions are work but not a grind. The calculator suggests a start for a 6 to 10 range: a weight you could lift about 8 times, so your first sets of 6 leave a couple of reps in reserve.
After the first session, stop going by the estimate and go by what you actually lift. That is the idea behind double progression: add reps until you reach the top of your range, then add weight.
Where ThreeByEight fits
ThreeByEight charts an estimated 1RM for each of your weighted lifts automatically, from the sets you log, so you can see the trend without testing a max. It does not set your targets from that number. It picks your next target from your last top set, and tells you why.
Next session’s target, with the reason.
iPhone app coming