One Rep Max Calculator
This one rep max calculator estimates the most you could lift for a single rep, from a set you've already done. Enter the weight and reps, pick pounds or kilograms, and you'll get your estimated 1RM from several formulas plus a full table of training loads by percent. Everything updates as you type, so it's easy to program your lifts. It's free and runs in your browser, so nothing you enter leaves your device.
- Estimated 1RM
- Four formulas
- Load table
- Pounds or kg
- Percent of max
Last updated June 17, 2026 Estimates only Reviewed by the Calcowa team
Enter a weight above zero and 1 to 20 reps.
Use a clean set you stopped a rep or two short of failure. A heavy set of 2 to 5 reps gives the sharpest estimate, since the formulas drift at high reps.
Your training loads
| % of max | Weight | Approx reps |
|---|
How do you find your one rep max?
Your one rep max, or 1RM, is the heaviest weight you could lift once with good form, and you don't have to actually attempt it to get a solid number. Instead you take a set you already did, say 225 pounds for 5 reps, and run it through a formula that maps reps to a percentage of your max. The Epley formula multiplies the weight by one plus the reps over 30, so that set estimates about 263 pounds. Brzycki, Lombardi, and McGlothin use slightly different curves and land a bit apart, which is normal, since each was fitted to different data. That's why this tool averages them for the headline figure rather than betting on one. Once you've got the max, the load table turns it into working weights: roughly 85 to 95 percent for heavy strength sets, 67 to 80 percent for muscle-building reps, and lighter loads for endurance. This tool runs every formula and builds the table the moment you type your set, so you can program your next session in seconds.
Estimating your max, step by step
Here's the quick routine after a working set, and it's just three steps:
- 1
Enter the setType the weight you lifted and the clean reps you got.
- 2
Pick the unitSwitch between pounds and kilograms to match your gym.
- 3
Read the maxSee your estimated 1RM and the load table for each percent.
Reps to percent of max
Here's the rough link between the reps you can do and the percent of your max, which is what the formulas are built on. It's an average, so don't treat it as exact, since it shifts a little by lift and by person.
| Reps | Percent of 1RM | Use |
|---|---|---|
| 1 | 100% | Max strength |
| 3 | 93% | Strength |
| 5 | 87% | Strength |
| 8 | 80% | Muscle |
| 10 | 75% | Muscle |
| 12 | 70% | Endurance |
Frequently asked questions
You enter the weight you lifted and how many clean reps you got, and it estimates the most you could lift once. It runs several proven formulas, Epley, Brzycki, Lombardi, and McGlothin, then averages them for a headline number. It also builds a table of training loads, showing the weight for each percentage of your max. Everything runs in your browser, so you'll see the numbers change as you type, and nothing you enter leaves your device.
You take a set you did short of failure and run it through a formula. The popular Epley version is weight times one plus reps divided by 30, so 225 pounds for 5 reps estimates about 263 pounds. Brzycki uses weight times 36 over 37 minus reps, which lands near 253. The estimates drift apart at high reps, which is why this tool averages a few of them for a steadier figure rather than trusting just one.
Fewer reps give a sharper estimate, so a heavy set of 2 to 5 reps works best. The formulas were fitted to lower-rep sets, and they lose accuracy as the reps climb, since endurance and form start to matter more than raw strength. A set of 10 or more can still give a ballpark, but don't lean on it for a true max. If you can, test with a weight you can move about 3 to 5 times with solid technique.
They're the share of your one rep max you use for different goals, and the table here turns them into real weights. Heavy strength work sits around 85 to 95 percent for low reps, hypertrophy training runs near 67 to 80 percent for moderate reps, and lighter endurance work falls below 65 percent. Knowing your max lets you set each session's weight on purpose instead of guessing, which is the whole point of estimating it in the first place.
A true max test is hard on the body, so it isn't something to do often or without preparation. This calculator is the safer route, since it estimates your max from a lighter set you can control. If you do test for real, warm up thoroughly, build up in steps, and use a spotter or safety bars. Treat the number as a tool for planning, not a goal to chase every session, and back off if your form breaks down. It's an estimate, not medical advice, so listen to your body over any chart.
Yes, it's completely free, with no sign-up, and it runs right in your browser, so nothing you enter leaves your device. Type the weight and reps from a recent set, switch between pounds and kilograms, and read your estimated max and load table in a tap. Bookmark it for programming your lifts, and remember it's an estimate, so let how the weight actually feels guide your training too.
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Programming your lifts?
Estimate your max above, then set heart rate zones for conditioning.