CALCULATOR
One Rep Max Calculator
Estimate your 1RM from any set, then get training loads at 95, 85, 75 and 65 percent for programming.
Most accurate at 1 to 6 reps taken close to failure. Accuracy falls off above 10 reps.
How one rep max estimates work
A one rep max is the heaviest weight you can lift once with good technique. Testing it directly is stressful, time consuming and carries injury risk, so most lifters estimate it from a set taken close to failure at a lighter load.
This calculator averages the Epley and Brzycki formulas, the two most widely used. Both are accurate within a few percent when the set is between one and six reps and genuinely close to failure. Above roughly ten reps the estimates drift, because fatigue tolerance and technique start to matter more than pure strength.
The percentage table is the practical output. Most training programmes prescribe loads as a percentage of 1RM, so an estimate turns any programme into actual numbers you can load on the bar.
The 1RM formulas
Example: 100 kg for 5 reps
100 x (1 + 5/30) = 116.7 kg
Example: 100 kg for 5 reps
100 x 36 / 32 = 112.5 kg
W is the weight lifted and R is the number of reps completed. Epley tends to read slightly higher as reps climb; Brzycki reads lower. This calculator averages the two, which is more robust than trusting either alone, and it is why the estimate sits between the two figures shown.
Reps to percentage of 1RM
| Reps to failure | Percent of 1RM | Primary adaptation |
|---|---|---|
| 1 | 100% | Maximal strength |
| 2 | 95% | Maximal strength |
| 3 | 93% | Strength |
| 5 | 87% | Strength and size |
| 8 | 80% | Hypertrophy |
| 10 | 75% | Hypertrophy |
| 12 | 70% | Hypertrophy and endurance |
| 15 | 65% | Muscular endurance |
Using percentages to programme training
Almost every structured strength programme prescribes load as a percentage of 1RM. Knowing your estimate turns an abstract programme into concrete numbers you can load on the bar, and it lets you progress systematically instead of guessing week to week.
Typical training blocks by percentage
| Goal | Percent of 1RM | Reps | Sets | Rest |
|---|---|---|---|---|
| Maximal strength | 85-95% | 1-5 | 3-6 | 3-5 min |
| Strength and size | 75-85% | 5-8 | 3-5 | 2-3 min |
| Hypertrophy | 65-80% | 8-12 | 3-4 | 60-90 sec |
| Endurance | 50-65% | 15+ | 2-3 | 30-60 sec |
Where estimates go wrong
- Sets not taken near failure. If you stopped with four reps left, the estimate is far too low. These formulas assume the set was genuinely hard.
- High rep sets. Beyond ten reps, fatigue tolerance and conditioning start to dominate, and individual variation widens sharply.
- Different exercises behave differently. Deadlifts typically show fewer reps at a given percentage than leg press, because the neural and technical demand is higher.
- Training age matters. Beginners generally get fewer reps at a given percentage than experienced lifters, because they cannot yet express their maximum efficiently.
- Technique breakdown is not a rep. Counting reps that lost position inflates the estimate and the injury risk that comes with acting on it.
Recalculate every four to six weeks rather than clinging to an old number. Strength changes, and programming against a stale 1RM either underloads your training or pushes you into weights you are not ready for.
Frequently asked questions
How accurate is a 1RM calculator?
Should I test my true one rep max?
Why do Epley and Brzycki disagree?
What percentage should I train at?
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General information, not medical advice. Consult a qualified professional before changing your diet, especially with a medical condition.