How to calculate your one-rep max, and when the estimate lies
Your one-rep max (1RM) is the heaviest load you can lift once with acceptable form. You do not need to test it. Take a hard set of 2 to 10 reps, put the weight and reps into the Epley formula, and you have an estimate that is usually within a few percent.
An estimate is enough to set training loads. It stops being reliable on high-rep sets and on isolation lifts, and it says nothing about a bad day. Treat it as a trend line, not a verdict.
The two common formulas
Epley:
1RM = w × (1 + r / 30)
Brzycki:
1RM = w × 36 / (37 − r)
Here w is the weight lifted and r is the number of reps you completed. Both were fitted to the same kind of data: sets taken close to failure on barbell lifts. They agree closely in the middle of the range and part ways at the ends.
A worked example: 80 kg for 8
Epley: 80 × (1 + 8/30) = 80 × 1.267 = 101.3 kg.
Brzycki: 80 × 36 / (37 − 8) = 2,880 / 29 = 99.3 kg.
The two answers differ by 2 kg. Round to the nearest plate you can load and call it 100 kg. The percent table below gives the same figure: 8 reps is about 80% of a max, and 80 / 0.80 = 100 kg.
If you work in pounds, the formulas are unchanged. Use 175 lb for 8 reps and you get roughly 222 lb by Epley.
Percent of 1RM, by reps
This is the common lookup table. It is the Brzycki curve rounded to whole percentages.
| Reps | % of 1RM | Load if 1RM is 100 kg |
|---|---|---|
| 1 | 100% | 100 kg |
| 2 | 95% | 95 kg |
| 3 | 93% | 93 kg |
| 4 | 90% | 90 kg |
| 5 | 87% | 87 kg |
| 6 | 85% | 85 kg |
| 8 | 80% | 80 kg |
| 10 | 75% | 75 kg |
| 12 | 70% | 70 kg |
| 15 | 65% | 65 kg |
Read it in either direction. If you know your max, it tells you what to load for a target rep count. If you know a set, it tells you the max behind it.
Why estimates drift
Above about 10 reps
The formulas are linear approximations of a curve that is not linear. Past 10 reps, the limit on your set stops being strength and becomes a mix of muscular endurance, breathing, grip and tolerance of discomfort. Two lifters with the same 1RM can differ by several reps at 65%. A set of 15 at 60 kg will usually produce a 1RM estimate that is too high or too low, and you cannot tell which without a heavy single.
Use sets of 10 or fewer when you want a number you can trust.
On isolation lifts
The percent table comes from compound barbell lifts: squat, bench, deadlift, press. On a lateral raise or a cable curl, a true one-rep max is not a meaningful quantity. The lever is short, the movement is easy to cheat, and the last rep depends on technique more than on strength. The formula will still return a figure. Do not plan around it.
When the set was not near failure
Both formulas assume the final rep was close to your limit. If you stopped 4 reps short, the estimate is low by a wide margin. Record RPE or reps in reserve with the set and read the number accordingly. See RPE and RIR for how to rate a set honestly.
Other sources of error
- Slow or paused reps give lower estimates than touch-and-go reps.
- Depth and lockout standards change between days and between gyms.
- Fatigue, sleep and food move the result by a few percent in either direction.
A single estimate has a margin of error. A line through six weeks of estimates is much harder to fool.
Using the number without testing a max
You can programme from an estimate and never load a true single. Three practical uses:
- Set working loads. For 4 sets of 5, load about 87% of your estimated max. For 3 sets of 8, about 80%. Start there, then adjust by feel and RPE.
- Choose a start for a new block. Take your best recent set, estimate the max, and begin the next block at 70 to 75% for sets of 8 to 10. Add load or reps from there.
- Check whether you are progressing. If the estimate from your top set rises over several weeks, the programme works. If it is flat over six weeks, look at sleep, volume and technique before changing the plan. See progressive overload for ways to move it.
Compare like with like. An estimate from 5 reps and an estimate from 12 reps are not the same measurement. Pick a rep range for the lift you care about and use that set as your reference.
If you do want a true max, run it when fresh, after a proper warm-up, with a spotter or safeties, and do not make it a weekly event. For most lifters it adds risk and little information.
In GymYuz
GymYuz shows an estimated 1RM, labelled e1RM, for each exercise, calculated from the sets you have logged. Because the estimate comes from real sets, you can read the strength curve for a lift and see whether your e1RM is rising, flat or falling over weeks. Log RPE or RIR on the set so you know how much to trust each point.
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