How to use the one rep max calculator
- Pick your units — pounds or kilograms. Every result is also converted to the other unit.
- Enter the weight and the reps of a hard set: the total load and the number of clean reps you completed. A set of 2 to 10 reps gives the best estimate.
- Say how close to failure you were (optional). If you stopped with two reps still in the tank, choose “2 more reps were possible”; the calculator counts the set as if you had kept going.
- Choose a formula for the main number, or keep the average of all seven. All seven estimates are always listed, along with how far apart they are.
The chart under the result turns your 1RM into training weights: each row gives a percentage, the exact weight, the weight rounded to what you can load with standard plates (5 lb or 2.5 kg steps), and roughly how many reps you can do with it.
The seven 1RM formulas
Each formula predicts the one-rep max from a weight w lifted for r reps to failure. They were fitted on different groups of lifters, which is why they disagree a little. Results for 100 kg × 5 reps:
| Formula | Equation | 100 kg × 5 |
|---|---|---|
| Epley (1985) | 1RM = w × (1 + r ÷ 30) | 116.7 kg |
| Brzycki (1993) | 1RM = w × 36 ÷ (37 − r) | 112.5 kg |
| Lander (1985) | 1RM = 100 × w ÷ (101.3 − 2.67123 × r) | 113.7 kg |
| Lombardi (1989) | 1RM = w × r0.10 | 117.5 kg |
| Mayhew et al. (1992) | 1RM = 100 × w ÷ (52.2 + 41.9 × e−0.055 × r) | 119 kg |
| O’Conner et al. (1989) | 1RM = w × (1 + 0.025 × r) | 112.5 kg |
| Wathan (1994) | 1RM = 100 × w ÷ (48.8 + 53.8 × e−0.075 × r) | 116.6 kg |
Epley and Brzycki are the two most used. They give exactly the same answer at 10 reps (both multiply the weight by 4/3), Brzycki is lower below 10 reps and higher above. Lombardi rises slowly and gives the lowest estimates for high-rep sets; Lander and Brzycki climb fastest. A single rep is already a one-rep max, so the calculator returns the weight itself for 1 rep instead of the small bonus some formulas would add.
Worked example
You bench press 225 lb for 5 reps to failure. Epley gives 225 × (1 + 5 ÷ 30) = 262.5 lb; Brzycki gives 225 × 36 ÷ 32 = 253.1 lb. The average of all seven formulas is 259.9 lb, and the seven estimates span 253.1 lb – 267.8 lb. In kilograms the same set — about 102 kg × 5 — points to a 1RM near 118 kg. If you had stopped at 5 reps with one more possible, the set counts as 6 reps to failure and every estimate goes up by about 2–3%.
One rep max percentage chart
For a 1RM of 259.9 lb (225 lb × 5), using the average of the seven formulas. The reps column is that same average solved for reps, so it tells you roughly how many reps a lifter with this max can do at each load:
| % of 1RM | Weight | Rounded to 5 lb | Reps (about) |
|---|---|---|---|
| 100% | 259.9 lb | 260 lb | 1 |
| 95% | 246.9 lb | 245 lb | 2 |
| 90% | 233.9 lb | 235 lb | 4 |
| 85% | 220.9 lb | 220 lb | 6 |
| 80% | 207.9 lb | 210 lb | 8 |
| 75% | 194.9 lb | 195 lb | 11 |
| 70% | 181.9 lb | 180 lb | 14 |
| 65% | 168.9 lb | 170 lb | 16 |
| 60% | 155.9 lb | 155 lb | 19 |
| 55% | 142.9 lb | 145 lb | 22 |
| 50% | 129.9 lb | 130 lb | 25 |
The National Strength and Conditioning Association’s textbook Essentials of Strength Training and Conditioning links loads to goals: at least 85% of 1RM for 6 reps or fewer to build maximal strength, 67–85% for 6–12 reps for muscle size (hypertrophy), and 67% or less for 12 or more reps for muscular endurance.
RPE and reps in reserve
RPE (rating of perceived exertion) on the 1–10 scale used in lifting is tied to reps in reserve (RIR): RPE 10 means no rep left, RPE 9 one rep left, RPE 8 two, and so on. RPE charts treat a set of 3 reps at RPE 8 like a set of 5 reps to failure, and the calculator does the same: reps done + reps in reserve. This lets you estimate your max from ordinary training sets without grinding to failure. Most people misjudge how many reps they have left by a rep or more, especially on high-rep sets, so be honest and conservative.
How accurate is an estimated 1RM?
For most lifters the estimate from a hard set of 3–6 reps lands within a few percent of a tested max. Accuracy drops with higher reps: a study by Mayhew and colleagues (2008) found the equations clearly more accurate when the set had fewer than 10 reps. The exercise matters too — when LeSuer and colleagues (1997) tested these seven equations on 67 college students, all of them underestimated the deadlift, while bench press and squat estimates were much closer. Endurance-trained lifters can do more reps at a given percentage, so their 1RM is overestimated; very strong, explosive lifters often get fewer reps, so theirs is underestimated.
The safest way to use the number is to plan training weights, not to chase a new record. If you test a true max, warm up thoroughly, work up in small jumps, and use a spotter, safety bars or a power rack. If you have an injury, high blood pressure or a heart condition, ask a doctor or a qualified coach before maximal lifting. For your energy needs on training days, see the TDEE calculator and the macro calculator.
Frequently asked questions
How do I calculate my one rep max?
Lift a weight you can handle for 3 to 10 clean reps, then enter the weight and the reps. With the Epley formula, 1RM = weight × (1 + reps ÷ 30): 100 kg for 5 reps gives 116.7 kg, and 225 lb for 5 reps gives 262.5 lb.
Which 1RM formula is the most accurate?
None is best for everyone. Epley and Brzycki are the most widely used and agree well between 3 and 10 reps; studies comparing the equations find that the best one changes with the exercise and the lifter. The average of all seven smooths out each formula’s bias, which is why it is the default here.
What percentage of my 1RM should I train with?
It depends on the goal: about 85% or more for 1–6 reps to build maximal strength, 67–85% for 6–12 reps to build muscle, and below 67% for 12 or more reps for endurance. Use the chart under the result to turn those percentages into plate-ready weights.
Is it safe to test a real one rep max?
It can be, for healthy lifters with good technique, a thorough warm-up and a spotter or safety bars. Beginners usually get more from estimating their max with this calculator than from testing it, because a true max attempt carries the highest risk of form breaking down.
Can I use a set I did not take to failure?
Yes. Choose how many reps you had left (RIR). Three reps with two more in the tank counts as five reps to failure. The estimate is only as good as your judgment of the reps you had left.
Last updated: October 19, 2026