How to estimate your one-rep max
Your one-rep maximum (1RM) is the most weight you can lift for a single clean repetition. Knowing it lets you set training loads precisely — but actually testing it carries real injury risk. Predictive formulas give you a close enough estimate from a set you can already do safely.
Why estimate instead of test?
A true 1RM test requires maximal effort against a weight you may never have handled before. Even with a spotter, pushing to a genuine limit increases the chance of technique breakdown and acute injury — particularly at the shoulder and lower back on pressing movements, and at the knee and hip on squats and deadlifts. The risk is highest when you are newer to the lift, because motor patterns are still being groomed.
Sub-maximal prediction solves this. You perform a set of 2–10 reps with a weight you know you can handle, then apply a formula to extrapolate the theoretical maximum. The result is an estimate — it will not match your true tested 1RM exactly — but for programming purposes it is accurate enough, and you stay out of the injury zone to get it.
The two most-used formulas
Epley formula
Developed by Boyd Epley at the University of Nebraska in 1985, this is probably the most widely cited predictive equation:
1RM = weight × (1 + reps ÷ 30)
It adds a fractional increment — one-thirtieth of the lifted weight per repetition — to the working load. The logic is that each additional rep you can grind out indicates a proportionally greater reserve capacity.
Brzycki formula
Matt Brzycki's 1993 equation uses a slightly different model based on a linear decline in percentage of 1RM per rep:
1RM = weight × 36 ÷ (37 − reps)
Brzycki and Epley tend to produce very similar results in the 1–5 rep range. As reps increase, they diverge; Brzycki approaches infinity as reps approach 37, so it becomes meaningless above about 12 reps. For sets of 10 or fewer, either formula is a reasonable choice.
Worked example
Say you complete 5 clean reps of the bench press with 185 lb and stop with a rep or two left in reserve — you did not grind to absolute failure.
Epley:
1RM = 185 × (1 + 5 ÷ 30) = 185 × 1.1667 ≈ 215.8 lb
Brzycki:
1RM = 185 × 36 ÷ (37 − 5) = 185 × 36 ÷ 32 = 185 × 1.125 = 208.1 lb
The two formulas bracket a range of roughly 208–216 lb. A practical approach: use the middle of that range, or pick one formula and use it consistently so your progress comparisons stay apples-to-apples.
Rep-range accuracy
Both formulas assume a relatively fresh, well-trained neuromuscular system and consistent technique. Accuracy degrades as reps climb for a few reasons:
- Fatigue effects accumulate. By rep 8 or 10, local metabolic fatigue is contributing to failure as much as maximal force capacity — the formula cannot distinguish the two.
- Fiber-type composition matters more at high reps. Individuals with a higher proportion of slow-twitch muscle fibers may complete many more reps at a given percentage of 1RM than the formula assumes, inflating the estimate.
- Technique degrades. At high rep counts, form changes alter the muscles being loaded, so the relationship between rep count and maximal strength becomes noisier.
As a practical rule: trust the estimate most when your test set falls between 2 and 6 reps. Use it as a rough guide when the set is 7–10 reps. Above 10 reps, treat the number as a ballpark only.
Using your estimated 1RM for programming
The main reason to know your 1RM is to set percentage-based training loads. Common strength programs prescribe work in terms like "3 sets of 5 at 80% of 1RM" or "5×5 at 75%." Once you have an estimated 1RM, these prescriptions become concrete numbers.
A few common percentage benchmarks for reference:
- 90–100% 1RM — maximal strength zone, low reps (1–3), high neural demand
- 75–85% 1RM — hypertrophy and strength overlap, moderate reps (4–8)
- 60–75% 1RM — hypertrophy and muscular endurance, higher reps (8–15)
Re-test your 1RM estimate every four to six weeks, or whenever you feel your working weights have shifted meaningfully. Do not try to re-estimate after a hard training day — you want a fresh set performed near your current capability.