About this one rep max calculator
Your one rep max (1RM) is the most weight you can lift for a single clean repetition of an exercise. Testing it directly means loading the bar near your limit, which is tiring and carries more risk of injury, especially without a spotter. A one rep max calculator estimates it from a lighter set instead: enter the weight you lifted and how many reps you completed, and the calculator predicts the weight you could lift once. This one runs six published formulas, shows each result, and averages them. It then gives you a percentage chart and the weight to use for a target number of reps. It works in pounds or kilograms, and everything runs in your browser.
How to use the 1RM calculator
- Enter the weight you lifted and the number of reps you completed with good form, from 1 to 30. Sets of 10 reps or fewer give the most dependable estimate.
- Choose lb or kg and a rounding step for the chart weights. A step of 5 suits a lb barbell with 2.5 lb plates on each side, and 2.5 suits kg plates.
- Optionally set a target rep count to see the weight that should take you to about that many reps.
- Click Estimate 1RM. The headline number is the average of the six formulas. The table shows each one so you can see the spread.
The six formulas
Each formula takes the weight (w) and the reps (r) and returns an estimated one rep max. They were fit to different groups of lifters, so they disagree a little, and the gap grows as the reps go up.
| Formula | 1RM estimate |
|---|---|
| Epley | w × (1 + r ÷ 30) |
| Brzycki | w × 36 ÷ (37 − r) |
| Lombardi | w × r0.10 |
| O’Conner | w × (1 + 0.025 × r) |
| Mayhew | w ÷ (0.522 + 0.419 × e−0.055 r) |
| Wathen | w ÷ (0.488 + 0.538 × e−0.075 r) |
For a single rep the answer is just the weight on the bar, so the calculator returns it unchanged. Epley and Brzycki give the same answer at 10 reps; below that, Epley comes out slightly higher.
Worked example: 225 lb for 5 reps
The default is 225 lb for 5 reps. Epley gives 225 × (1 + 5 ÷ 30) = 262.5 lb. Brzycki gives 225 × 36 ÷ 32 = 253.1 lb. O’Conner gives 225 × 1.125 = 253.1 lb. The other three land between 262 and 268 lb, and the average of all six is about 260.5 lb. With rounding to the nearest 5 lb, that is a 1RM of roughly 260 lb, and 90% of it is about 235 lb.
How accurate is a 1RM estimate?
- Fewer reps is better. The formulas were built mostly around sets of about 10 reps or fewer. A set of 20 or 30 reps depends heavily on endurance and pacing, so treat those estimates as rough.
- It varies by person and lift. Reference sources note that an estimate can be off by 10% or more, and that formulas tend to suit experienced lifters better than beginners, whose true max may be lower.
- Technique counts. Only count reps with the same range of motion and form you would use in a real max attempt, such as a bench press with a pause, or a squat to proper depth.
- Different exercises behave differently. A formula that fits a bench press may over- or under-predict a deadlift or a curl.
Use the number as a starting point for planning, not as a promise. If you plan to test a true max, warm up thoroughly, use a spotter or safety bars, and build up in small jumps.
Using your 1RM in training
Many strength programs describe sets as a percentage of your 1RM: 3 sets of 5 at 80%, or a heavy single at 90%. Some programs work from a “training max” set a little below the true max, often around 90%, to leave room for good form and steady progress. The percentage chart above converts your estimated 1RM into weights for each step from 100% down to 50% and shows how many reps that weight typically allows. The “weight for target reps” box answers the reverse question: how heavy should I go to get about 8 reps?
Planning meals around your training? Try the TDEE Calculator, the Macro Calculator or the Calorie Calculator, and convert plates with the Pounds to Kilograms converter.
This tool gives estimates for general fitness planning only and is not medical or coaching advice. If you have an injury or a health condition, check with a qualified professional before lifting near your maximum.
Frequently asked questions
Pick a set you completed with good form, then apply a formula. The Epley formula is weight x (1 + reps / 30), so 225 lb for 5 reps gives 225 x (1 + 5 / 30) = 262.5 lb. The calculator also runs Brzycki, Lombardi, O'Conner, Mayhew and Wathen, then averages all six.
No single formula wins for everyone. They were fit to different groups of lifters and exercises. Epley and Brzycki are the most widely used and match at 10 reps. Using the average of several formulas smooths out the differences, and estimates from sets of 10 reps or fewer are more reliable than from sets of 20 or more.
Use a hard set of about 3 to 8 reps taken close to failure with strict form. Very low rep sets are nearly a max already, and sets above about 10 reps depend more on muscular endurance, which makes the estimate less accurate.
Estimating from a lighter set avoids the load and fatigue of a true max attempt, so it is generally less risky. It is still only an estimate. If you do test a real max, warm up well, use a spotter or safety bars, and increase the weight in small steps.
Multiply your 1RM by the percentage in your program. If your 1RM is 260 lb, 80% is 208 lb, which rounds to 210 lb on a barbell with 2.5 lb plates. The percentage chart in this tool does the math for every 5% step from 100% to 50%.
No. The formulas scale with the weight, so the same set in kilograms gives an answer in kilograms. Pick lb or kg for the labels and the rounding step. For example, 100 kg for 5 reps gives an Epley estimate of 116.7 kg, which is about 257 lb.