One Rep Max Calculator
Free one-rep max calculator. Estimate your 1RM from any set with Epley and Brzycki formulas, plus working-set percentages. No signup.
Estimate a one-rep max without testing it
This tool predicts the heaviest weight you could lift once, based on a set you have already completed. Enter the weight and the reps, and it returns two estimates plus a planning number and a full table of working weights.
The two formulas
The calculator runs both of the standard rep-max equations and shows each result:
- Epley: 1RM = weight × (1 + reps ÷ 30)
- Brzycki: 1RM = weight × 36 ÷ (37 − reps)
A planning figure is the average of the two, which smooths out the disagreement between them. The working-weight table is generated from the Epley estimate at 95, 90, 85, 80, 75, 70, 65, 60, and 50 percent.
Worked example with the default inputs
The tool opens with 225 lb lifted for 5 reps, in pounds.
- Epley = 225 × (1 + 5 ÷ 30) = 225 × 1.1667 = 262.5 lb
- Brzycki = 225 × 36 ÷ (37 − 5) = 8,100 ÷ 32 = 253.1 lb
- Planning estimate = (262.5 + 253.1) ÷ 2 = 257.8 lb
| Intensity of 1RM | Weight from the Epley estimate |
|---|---|
| 95% | 249.4 lb |
| 90% | 236.3 lb |
| 85% | 223.1 lb |
| 80% | 210 lb |
| 75% | 196.9 lb |
| 70% | 183.8 lb |
| 65% | 170.6 lb |
| 60% | 157.5 lb |
| 50% | 131.3 lb |
An interesting detail: Epley and Brzycki return identical answers at exactly 10 reps, because the two equations cross there. Below 10 reps Epley tends to read slightly higher, which is why the tool shows both.
Reading the rep-max relationship
The percentage table doubles as a rep guide if you invert it. As a rough rule, a weight you can lift for 5 reps is about 87% of your 1RM, 8 reps about 80%, and 12 reps about 70%. That is why a heavy set of five programs around 85–90% of the estimate, while a set of ten sits nearer 75%.
How to program from the estimate
Heavy strength work usually sits at 85–90% of 1RM for low reps and long rests. Hypertrophy work clusters around 65–80% for moderate reps. Power and speed sets use 50–65% moved explosively. Re-estimate every four to six weeks, because the number moves as you train. If you plan to test a true single, load the bar at roughly 90% of the estimate for a final warm-up, then add conservatively.
Common mistakes
- Using a set that was not near failure. The formulas assume few reps in reserve; an easy 5-rep set inflates the estimate.
- Extrapolating past about 10 reps. Accuracy falls away as rep counts climb, so a 20-rep set can badly overestimate a max.
- Mixing units mid-table. The percentages inherit whatever unit you selected, so pick pounds or kilograms before reading the table.
- Testing a max too often. True singles are taxing and carry injury risk; estimate most of the time.
How accurate is a one-rep max calculator?
For sets of 10 reps or fewer, expect the estimate to land within roughly 5–10% of a tested max. Technique, fatigue, and bar speed all shift the real number, so treat the result as a programming guide rather than a record.
Why are the Epley and Brzycki numbers different?
The two equations were fitted on different data sets, so they weight high-rep and low-rep efforts differently. Averaging them is a pragmatic middle ground. If you consistently train in one rep range, you can lean toward the formula that matches it.
Should I use pounds or kilograms?
Use whatever your gym plates are marked in. The formulas are unit-agnostic: they scale a chosen weight, so the output carries the same unit as the input.
Can I estimate a max from a set that is not near failure?
Only loosely. The formulas assume the set ended close to failure, roughly one to three reps in reserve. A comfortable set of five might leave ten in reserve, which would overstate the max considerably. Take the working set to within a rep or two of failure for a usable estimate.
Which formula should I trust more?
Neither is universally better. Epley tends to read a little high on low-rep sets, and Brzycki a little low on high-rep sets. The average the tool reports is a reasonable compromise; if you regularly train heavy singles, use the Epley line, and if you train higher reps, lean on Brzycki.
Strength numbers pair naturally with body composition. The body fat calculator shows the tissue behind the lifts, including lean body mass, and to fuel the training block, start from the TDEE calculator.