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.
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 100 x (1 + 5/30) = 116.7 kg. The alternative Brzycki formula is 1RM = weight x 36 / (37 - 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.
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.
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.
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 their own branded 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.
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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