Tool
1RM calculator
This 1RM calculator estimates a one-rep max from a single set: enter the weight, the reps and the reps you had left. It calculates as you type, stores nothing, and there is no account step.
The RIR field is here for a specific reason. The formula assumes the set ended at failure, and most training sets do not. Without that field a calculator reads low for anyone who trains with reps in reserve.
Reps you had left. Zero if the set went to failure.
Estimated one-rep max
112.5 kg
Calculated from 5 reps to failure.
Working: 100 × 36 / (37 - 5) = 112.5
The formula behind this 1RM calculator
1RM = weight × 36 / (37 - reps)
Load7 uses Brzycki, the same formula in the calculator, in your stats and in the AI coach. There are not two different numbers for one question.
A set of 100 kg for 5 reps to failure gives 100 × 36 / 32, so 112.5 kg.
Stop that same set two reps short and the arithmetic changes. Two reps in reserve means the set had 7 reps in it, so the estimate runs on 7 instead of 5: 100 × 36 / 30, or 120 kg. That is a 7.5 kg gap on a single set, and it is the most common reason a calculator disagrees with the bar.
Percentage of 1RM by rep count
The same formula solved for weight. Multiply your 1RM by the percentage to get a working weight, or read it backwards to see what a given set implies.
| Reps | % of 1RM |
|---|---|
| 1 | 100% |
| 2 | 97.2% |
| 3 | 94.4% |
| 4 | 91.7% |
| 5 | 88.9% |
| 6 | 86.1% |
| 7 | 83.3% |
| 8 | 80.6% |
| 9 | 77.8% |
| 10 | 75% |
| 11 | 72.2% |
| 12 | 69.4% |
These values are generated by the same formula the calculator uses, so the table cannot drift away from it.
Where the estimate breaks down
Four things this number will not do for you:
- It assumes failure. A set you stopped short of reads low until you fill in the RIR field.
- It drifts above 10 reps. Brzycki was fitted on low-rep sets and by 15 it reads noticeably low. Treat anything past ten reps as a direction rather than a number to program from.
- It does not know which lift you did. Rep capacity at a given percentage varies by movement: at 80% most people grind out more reps on a leg press than on a deadlift. One formula cannot carry that.
- One session is not a trend. e1RM moves with sleep, food and where you sit in a block. The signal is the direction across three or four weeks, not today’s figure.
FAQ
How do you calculate a 1RM?
Put the weight and reps into the Brzycki formula: 1RM = weight × 36 / (37 - reps). A set of 100 kg for 5 reps to failure gives 100 × 36 / 32, so 112.5 kg. If the set did not end at failure, add the reps you had left: 5 reps at 2 RIR counts as 7.
How accurate is a 1RM calculator?
On sets of 5 reps or fewer taken to failure, the estimate usually lands within a few percent of a tested max. Above 10 reps the error grows and Brzycki starts reading low. The largest source of error is not the formula though, it is entering sets that stopped short of failure as if they were taken to failure.
Does the calculator work in pounds?
Yes. The formula scales linearly, so pounds in gives pounds out. Nothing on this page converts between units, the toggle only changes the label on the result.
What is e1RM?
e1RM is an estimated one-rep max, a 1RM worked out from an ordinary working set rather than measured with a maximal attempt. It lets you watch strength weekly without paying the fatigue cost of testing a true max.
Should I test a true 1RM instead?
Rarely, unless you compete. A max attempt costs several days of recovery and returns one number, while an e1RM trend from working sets returns a dozen in the same period. Testing makes sense before a meet or at the end of a strength block, when you are cutting volume anyway.
Further reading
- e1RM: What an Estimated 1RM Actually Tells YouHow to read an e1RM trend, why a single session means nothing, and where the estimate stops being trustworthy.
- RIR vs Training to Failure: What the Data SaysProximity to failure affects size and strength differently. How to set RIR on compounds and isolations so you stop paying fatigue for nothing.
- Adjusting Training for Downward e1RM Trend: Recovery over GritLearn how to handle a 3-week downward e1RM trend by tactically adjusting accessory volume while maintaining high-intensity loads for strength.
- Solving the RPE vs RIR Mismatch in Strength TrainingLearn how to fix the RPE vs RIR mismatch in strength training. Use the Set-Drop protocol to reduce fatigue without losing strength adaptations.
Load7 works this out after every set
This calculator handles one set. Load7 estimates e1RM from every set you log and charts the trend per lift, so you read a direction rather than a single figure. Logging and stats are free.