One Rep Max Calculator

Your one-rep max (1RM) is the heaviest weight you can lift for a single repetition with proper form. Almost every powerlifting and bodybuilding programme references 1RM percentages: '5 sets of 5 at 80%', '3 sets of 8 at 70%' and so on. Without knowing your 1RM, those instructions are guesses. Testing 1RM directly is risky and often pointless for most lifters; estimating it from sub-maximal sets is far safer and almost as accurate.

The calculator takes a recent set you actually completed (e.g. 100 kg for 8 reps) and runs it through three independent formulas to estimate your true 1RM. The formulas are well-validated for the 2 to 10 rep range; above 10 reps the estimates start to drift because muscular endurance starts to dominate over pure strength. For best results, plug in a set you took to failure (or one rep short of it) at between 4 and 8 reps.

The Epley formula (1RM = weight x (1 + reps/30)) is the most common in bodybuilding programmes. It tends to give slightly conservative estimates at low reps and slightly optimistic ones at high reps. Brzycki (1RM = weight x 36 / (37 - reps)) is the powerlifting standard, more accurate at low reps (3 to 6) where the relationship between strength and reps is closest to linear. Lombardi (1RM = weight x reps^0.10) gives a third estimate based on a power-law model.

All three formulas agree closely at 5 reps; they diverge most at 1 rep (where the estimate equals the input weight) and at 12+ reps (where reliability drops). The calculator shows all three so you can see the spread. If they disagree by more than 5 to 10%, your input set was probably too easy or too close to true failure for the formulas to work cleanly. Re-test with a 5 to 8 rep set.

The percentages table below your 1RM estimate is the workhorse part of the tool. A 5x5 strength programme calls for 80 to 85%; an 8 to 10 hypertrophy session for 65 to 75%. A heavy single (the 'today's top set' in some programmes) is 90 to 95%. Knowing your 1RM gives you the actual weight to load on the bar, not just a rep target with no anchor.

The table also shows estimated reps achievable at each percentage, which lets you sanity-check the load. If your estimated 1RM says 100 kg and the table says 80% (80 kg) should be good for 6 to 8 reps, but you are only getting 4 reps with form, your real 1RM is lower than the calculator suggests. This is most common with deadlifts, where rep-based estimates over-predict 1RM by 10 to 20% because the deadlift fatigues the central nervous system more aggressively than other lifts.

Genuinely testing your 1RM is high-risk and high-fatigue. You need a fully warmed-up nervous system, a competent spotter, several attempts to find the true ceiling and significant recovery time afterwards. For competitive powerlifters, this is part of the sport; for everyone else, the marginal accuracy gain over a calculator is not worth the injury risk and the lost training time. A single missed lift can cost you a week of training while you nurse a strain.

Use the calculator instead. Plug in a recent solid set, take the average of the three formulas, and use that as your working 1RM for the next 4 to 6 weeks of programming. Re-test (with a sub-maximal set, not a true 1RM) every 6 to 8 weeks to track progress. The [protein intake calculator](/protein-intake-calculator) and [TDEE calculator](/tdee-calculator) help you set the nutrition side of strength training, which usually limits gains more than the lifting itself.