What your estimated 1RM is actually telling you
Your e1RM is not a prediction of what you'd lift on a max attempt. Here is what the number really measures, and how to read it properly.
Founder of Vertex Strength LabPublished · Updated
Short answer
An estimated 1RM (e1RM) converts a set's weight and reps into the single-rep load it corresponds to, usually with the Epley or Brzycki formula. It is most reliable from sets of 1 to 8 reps taken close to failure and gets noisy past 12 reps. Use it to track your strength trend and choose loads, not to predict a max attempt.
Your estimated 1RM is the number VERTEX shows climbing on your strength chart. It is also the number most people misread.
It is not a promise that you could walk into the gym tomorrow and hit that weight for a single. It is a common unit that lets you compare a set of 5 in March against a set of 8 in July, and tell whether you actually got stronger in between. That is a genuinely useful thing. It is just not the thing most people think it is.
1–8 reps
The range where the estimate is worth trusting
14 kg
How far two respectable formulas disagree at 15 reps
Where the number comes from: the Epley and Brzycki formulas
You lift a weight for a number of reps. A formula converts that pair into the single-rep load it corresponds to (the 1RM calculator runs both of the standard ones). The two that almost every app and spreadsheet uses were published decades ago (Epley 1985; Brzycki 1993) and fitted to real lifting data:
- Epley:
1RM = weight × (1 + reps / 30) - Brzycki:
1RM = weight × 36 / (37 − reps)
Both take the same input and both give you a number. They do not give you the same number.
The formulas disagree, and the gap tells you something
Here is what each formula returns for a 100 kg lift at different rep counts:
| Reps | Epley | Brzycki |
|---|---|---|
| 1 | 103 kg | 100 kg |
| 3 | 110 kg | 106 kg |
| 5 | 117 kg | 113 kg |
| 8 | 127 kg | 124 kg |
| 10 | 133 kg | 133 kg |
| 12 | 140 kg | 144 kg |
| 15 | 150 kg | 164 kg |
Two things stand out.
They agree exactly at 10 reps — a coincidence of how the two curves were fitted, not a sign that 10 reps is the accurate zone. And they diverge in opposite directions on either side of it: below 10 reps Brzycki is the conservative one, above 10 reps it runs away, predicting 164 kg from a set of 15 where Epley says 150 kg.
Notice also that Epley at one rep returns 103 kg for a 100 kg single. The formula does not know that a single is the max. That is your first clue about how much precision is really on offer here.
The gap between the two formulas.
How far apart the two standard estimates land at each rep count. They cross at ten and diverge in opposite directions either side of it.
1 rep
3 kg apart
5 reps
4 kg apart
10 reps
they agree
12 reps
4 kg apart
15 reps
14 kg apart
The disagreement between two respectable formulas at 15 reps is 14 kg. That is the error bar. Any number you read off a high-rep set is carrying it.
How accurate is an estimated 1RM? The rep range you can trust
The rule is simple: the further the set is from a single, the more the formula is guessing.
Four zones, by rep count.
1–5 reps
Tight
Both formulas land within a couple of percent of each other and of reality. If you need a number you can act on, take it from here.
6–8 reps
Solid
The sweet spot for most people — heavy enough to be informative, not so heavy that you need a spotter and a good night's sleep to run one.
9–12 reps
Getting noisy
Usable for tracking a trend, not for planning attempts. Fine as long as you compare it only against other sets in the same range.
13+ reps
A fitness marker, not a strength one
At this range you are measuring muscular endurance as much as maximal force, and the formulas were never good here.
The caveat that matters more than the formula
Every one of these formulas assumes the set was taken close to failure.
This is the part that quietly wrecks most people's data. Ten reps with two left in the tank and ten reps where the last one took six seconds and a lot of noise are the same input to the formula and completely different events in your body. The formula cannot see the difference. It will hand you an e1RM either way, and one of them will be wrong by a wide margin.
If you stop your sets well short of failure — which is often the correct training decision — your e1RM will systematically understate you. That is fine, as long as you are consistent. A number that is reliably 5% low still shows you a real trend. A number that is 5% low some weeks and accurate on others shows you nothing but noise.
Consistency
A number that is reliably 5% low still shows you a real trend. A number that is 5% low some weeks and accurate on others shows you nothing but noise. Log your sets the same way, take them to a similar proximity to failure, and the trend line becomes trustworthy even if any individual point is not.
What to actually do with it
- Read the slope, not the point. One session's e1RM is a data point with an error bar. Six weeks of them is a signal. The question worth asking is never "what is my e1RM today" — it is "is this line going up."
- Compare like with like. Your bench e1RM from a set of 5 and from a set of 12 are not interchangeable readings. Where you can, track the estimate from a consistent rep range.
- Use it to pick loads. This is what it is genuinely good at. If your e1RM says 120 kg and your program calls for a set at 75%, you have a defensible starting point at 90 kg instead of a guess. The 1RM calculator prints the full percentage table from any set.
- Don't test a real max to validate it. A true 1RM attempt is a high-fatigue, non-trivial-risk event that buys you one data point. It does not make your training better. If you are not competing in a sport that requires one, you almost certainly do not need one.
- Let plateaus mean something. If the line has been flat for six weeks, that is real information about your programming, recovery, or nutrition. It is not a reason to test your max — it is a reason to change something upstream.
"I should test my real max to find out if the estimate is right."
Costs more than it tells you
Key numbers
| Reps in the set | Reliability | Use it for |
|---|---|---|
| 1–5 | Tight | Planning loads |
| 6–8 | Solid | Planning loads and tracking the trend |
| 9–12 | Noisy | Tracking the trend only |
| 13+ | Poor | Muscular endurance, not maximal strength |
At 15 reps on 100 kg, Epley and Brzycki disagree by 14 kg.
The short version
Your e1RM is a well-calibrated ruler with a slightly fuzzy zero point. It measures change extremely well and absolute strength only roughly. Track it from sets of 5 to 8 taken near failure, log honestly, and watch the trend over months rather than sessions.
That is the whole game. The number climbing is the point. The number itself is just the unit it climbs in.
Common questions
How is estimated 1RM calculated?
A formula converts one set's weight and reps into a single-rep load. Epley is weight × (1 + reps ÷ 30) and Brzycki is weight × 36 ÷ (37 − reps). VERTEX uses Epley.
Which is more accurate, Epley or Brzycki?
Neither is best for everyone. They stay within a few kilos of each other up to about 12 reps and diverge after that: at 15 reps on 100 kg, Brzycki predicts 164 kg and Epley 150 kg. Pick one and use it consistently.
Why is my estimated 1RM lower than what I can actually lift?
Most likely because your sets stop short of failure. The formulas assume a set taken close to failure, so leaving reps in reserve makes the estimate read low. If you stop at the same point every time, the trend is still accurate.
Do I need to test my real 1RM?
Only if you compete. A true max attempt buys one data point at the cost of several days of fatigue and some risk. Tracking an estimate from hard sets of 5 to 8 is enough.
How many reps give the most accurate 1RM estimate?
Sets of 1 to 5 reps are the tightest, and 6 to 8 is a good balance between accuracy and effort. Past about 12 reps the estimate mostly reflects muscular endurance.
References
- Epley B. Poundage Chart. Boyd Epley Workout. Lincoln, NE: Body Enterprises; 1985.
- Brzycki M. Strength Testing: Predicting a One-Rep Max from Reps-to-Fatigue. Journal of Physical Education, Recreation & Dance. 1993;64(1):88–90. doi:10.1080/07303084.1993.10606684