One rep max calculator.
Estimate your 1RM from any working set, then get a full percentage-of-1RM table you can program every lift from. Uses the Epley formula by default, with Brzycki as a one-tap alternative. Works in pounds or kilograms.
By Markus Evers Updated June 27, 2026 Method: Epley + Brzycki 1RM formulas
Sources
- Epley B (1985), Boyd Epley Workout (poundage chart)
- Brzycki M (1993), Journal of Physical Education, Recreation and Dance
estimate your 1rm
Formula
263 lb
| % of 1RM | Working weight | Est. reps |
|---|---|---|
| 100% | - | - |
| 95% | - | - |
| 90% | - | - |
| 85% | - | - |
| 80% | - | - |
| 75% | - | - |
| 70% | - | - |
| 65% | - | - |
| 60% | - | - |
Working weights are rounded to the nearest 5 lb / 2.5 kg for the gym. Estimated reps are an inverse of the same formula and are a guide, not a guarantee.
the short answer
A one rep max calculator estimates the heaviest weight you could lift once from a set you already did. The Epley formula is 1RM = weight x (1 + reps / 30). Lift 100 kg for 5 reps and your estimated 1RM is 116.7 kg. Brzycki is the alternative: 1RM = weight x 36 / (37 minus reps).
What a one rep max is and how it is calculated.
Your one rep max (1RM) is the most weight you can lift for a single, full repetition of an exercise. Testing a true max is taxing and not always safe - dialling in your overhead press form before chasing a heavy single keeps the attempt clean - so coaches estimate it from a submaximal set instead. Both formulas in this calculator take the weight you lifted and how many reps you got, and project upward to a single rep.
The Epley formula is 1RM = weight x (1 + reps / 30). The Brzycki formula is 1RM = weight x 36 / (37 - reps). They agree closely in the 1-to-5-rep range and diverge as reps climb - Epley reads a touch higher, Brzycki a touch lower - which is why having both matters. Estimates are most reliable at low reps and lose accuracy past about 10, because endurance and fatigue start to dominate.
Once you have a 1RM, the percentage table is the real payoff. Multiplying the max by 90%, 80%, or 70% gives you concrete working weights for heavy singles, strength work, and volume - so a single tested number programs an entire training block.
What is the Epley formula and where does it come from?
Epley: 1RM = weight x (1 + reps / 30), from Boyd Epley's 1985 poundage chart at the University of Nebraska. Brzycki: 1RM = weight x 36 / (37 - reps), from Matt Brzycki's 1993 article on predicting a one-rep max from reps to fatigue. Both are estimates from a submaximal set, and both are the formulas this calculator runs. The table gives the multiplier for each rep count so you can do it in your head: multiply the weight you lifted by the number in the row.
Worked example, the one people ask most: squat 225 for 8 clean reps. Epley gives 225 x 1.267 = 285; Brzycki gives 225 x 1.241 = 279. The two agree within 2 percent up to 10 reps and drift apart after that, which is why the accuracy note above treats sets past 10 reps as rough.
| Reps | Epley multiplier | Brzycki multiplier | 100 kg lifted, Epley 1RM | 225 lifted, Epley / Brzycki |
|---|---|---|---|---|
| 1 | x 1.033 | x 1.000 | 103.3 | 233 / 225 |
| 2 | x 1.067 | x 1.029 | 106.7 | 240 / 231 |
| 3 | x 1.100 | x 1.059 | 110.0 | 248 / 238 |
| 4 | x 1.133 | x 1.091 | 113.3 | 255 / 245 |
| 5 | x 1.167 | x 1.125 | 116.7 | 262 / 253 |
| 6 | x 1.200 | x 1.161 | 120.0 | 270 / 261 |
| 7 | x 1.233 | x 1.200 | 123.3 | 278 / 270 |
| 8 | x 1.267 | x 1.241 | 126.7 | 285 / 279 |
| 9 | x 1.300 | x 1.286 | 130.0 | 292 / 289 |
| 10 | x 1.333 | x 1.333 | 133.3 | 300 / 300 |
Sources as cited in the method note above: Epley, B. (1985), Poundage Chart, Boyd Epley Workout, Lincoln, NE; Brzycki, M. (1993), Strength testing: predicting a one-rep max from reps-to-fatigue, Journal of Physical Education, Recreation and Dance, 64(1), 88 to 90.
Programming a whole block from one number.
Strength coaches rarely test a true max every week. They estimate it from a recent top set, then prescribe load as a percentage of that 1RM: heavy singles at 90-95%, primary strength work at 80-85%, and accessory or volume sets at 65-75%. The percentage table above turns one estimate into the load for every set in the program. Those load bands line up with the rep ranges you program for each goal, from low-rep strength work to higher-rep volume.
The power move is keeping each client's 1RM current. When a lifter hits a new estimated max, every percentage recalculates and the whole block scales up automatically. That is the difference between a static spreadsheet and a program that progresses with the athlete - and it is exactly the kind of target coaches set per client inside their coaching software.
Turn the estimate into a 4-week block
Paste the estimated 1RM and the percentage table the calculator prints and the model lays out four weeks of sets, reps and loads at those percentages with a deload and a retest rule; it is told not to change the number. The wider workflow is ChatGPT for programme design as a coach.
Turn the estimate into a 4-week block
When to use it: After the estimate, when you write the next block for that lift.
What to paste in: The 1RM, the weight and reps it came from, the percentage table, a client ID, training age and goal.
This one rep max calculator estimates a client's [LIFT] 1RM at [1RM] kg from [WEIGHT] kg for [REPS] reps (client ID [ID], no name, training age [YEARS], goal [GOAL]). Using the percentage table from the calculator ([PASTE THE PERCENTAGE ROWS]), write a 4-week block for this lift: sets, reps and load each week at the stated percentages, with week 4 as a deload at 60 to 65 percent, and the rule for when to retest. Do not change the 1RM, do not add other exercises, and do not exceed 90 percent in week 3. If the training age or goal changes the block, say how and ask me before assuming.
Set targets like this for every client - automatically.
This calculator is a handy one-off. Coachway lets coaches set strength targets per client and program off them inside a workout builder with 1,800+ exercises, supersets, per-set logging, and PR tracking - so when a client hits a new max, the next block reflects it. Clients follow the plan and log lifts in the client app.
Coachway is the operating system for online fitness and nutrition coaches. See how it fits your client list on the pricing page, or book a 15-minute demo.
Frequently asked questions.
How do you use a one rep max calculator?
Enter the weight you lifted and the number of clean reps you completed, then pick a formula. The one rep max calculator applies the Epley equation (1RM = weight x (1 + reps / 30)) by default and returns your estimated single-rep max, plus a percentage table of working weights so you can program every set off one number.
What is the Epley formula for one rep max?
The Epley formula is 1RM = weight x (1 + reps / 30). If you lift 100 kg for 5 reps, that is 100 x (1 + 5/30) = 116.7 kg estimated. It is the most widely used estimate because it stays accurate in the low-to-moderate rep range where most strength training sits.
Epley vs Brzycki - which formula should I use?
Epley (1RM = w x (1 + reps/30)) and Brzycki (1RM = w x 36 / (37 - reps)) agree closely at low reps and diverge as reps climb. Epley reads slightly higher at high reps, Brzycki slightly lower. For sets of 1 to 10 reps either is fine; test both and use the one that matches your lifters.
How accurate is an estimated one rep max?
Estimated 1RM is most accurate at 1 to 5 reps and drifts as the rep count rises, because fatigue and lifter endurance vary. Treat it as a training guide, not a tested max. Re-estimate from recent sets and have clients confirm with a real top single only when it is safe and supervised.
How do coaches program with a 1RM percentage table?
Coaches anchor a block to one estimated 1RM, then assign load as a percentage - heavy singles at 90-95%, strength work at 80-85%, and volume at 65-75%. The percentage table turns one number into every working set, so the whole program scales the moment a lifter hits a new max.
Should I calculate one rep max in kg or pounds?
Either - the math is identical because both formulas are ratios. This one rep max calculator lets you switch between pounds and kilograms, converts internally, and returns the result in the unit you chose, so US lifters can stay in pounds and the percentage table follows the same unit.
Is an ORM calculator the same as a one rep max calculator?
Yes - this ORM calculator and a one rep max calculator are the same tool, because ORM is simply the common abbreviation for one rep max. Enter the weight you lifted and your clean reps, pick the Epley or Brzycki formula, and the ORM calculator returns your estimated single-rep max plus a percentage-of-1RM table of working weights. Whether you type "ORM" or "one rep max", you land on the same estimate and the same programming table, and you can switch between pounds and kilograms without changing the result.
What is the source of the Epley formula 1RM = weight x (1 + reps / 30)?
The Epley formula, 1RM = weight x (1 + reps / 30), comes from strength coach Boyd Epley, whose 1985 poundage chart (the Boyd Epley Workout) is the source this calculator cites in its method note above. Lift 100 kg for 5 reps and it estimates 100 x (1 + 5/30) = 116.7 kg. Epley's equation became the most widely used 1RM estimate because it stays accurate in the low-to-moderate rep range where most strength training sits, which is why this tool applies it by default and offers Brzycki as the alternative.
If I can squat 225 for 8 reps, what is my max?
About 285 by the Epley formula (225 x (1 + 8 / 30) = 285) and about 279 by Brzycki (225 x 36 / (37 - 8) = 279). Treat 280 to 285 as the estimate and program percentages off it rather than testing the single. The multiplier table above gives the same answer for any weight and rep count from 1 to 10.
What is the Brzycki formula and where does it come from?
1RM = weight x 36 / (37 - reps), published by Matt Brzycki in 1993 in the Journal of Physical Education, Recreation and Dance as a way to predict a one-rep max from reps to fatigue. It reads slightly lower than Epley above 5 reps and is undefined at 37 reps, which is why the calculator accepts up to 36 reps and why estimates past 10 reps should be treated as rough.
Can ChatGPT program from a one rep max?
It can turn the estimate and the percentage table into a four-week block of sets, reps and loads with a deload and a retest rule, which is the arithmetic part of programming. It cannot see the client's technique or bar speed, so keep the loads as prescribed percentages and adjust from the first week's logs; the prompt on this page tells it not to change the 1RM or add exercises.
Estimated maxes are a training guide, not a tested result, and they lose accuracy at high reps - confirm a true max only when it is safe and supervised. This tool is general fitness information, not medical advice.
Keep building the plan: try the macro calculator and TDEE calculator for the nutrition side, then read how coaches turn these numbers into programming in how to calculate TDEE and macros for clients and our guide to software for strength and conditioning coaches.
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