🏋️ One Rep Max (1RM) Calculator
By ToolNimba Health Team · Reviewed by ToolNimba Editorial Review, strength training content · Updated 2026-06-19
This calculator gives an estimate only. A predicted one rep max is not the same as a tested max, and it grows less accurate as the rep count rises. Attempting a true maximal lift carries injury risk: warm up properly, use correct form, and have a spotter or safety bars. If you are new to lifting, recovering from injury, or have a health condition, speak to a qualified coach or doctor before testing heavy loads. This is general information, not medical or coaching advice.
| % of 1RM | Weight | Typical reps |
|---|
Your one rep max (1RM) is the heaviest weight you can lift for a single repetition of an exercise such as the squat, bench press or deadlift. It is the standard yardstick for programming strength work, because most training plans prescribe loads as a percentage of it. Testing a true 1RM is risky and tiring, so this calculator estimates it from a set you have already done: enter the weight you lifted and how many clean reps you got, and it returns your predicted 1RM using both the Epley and Brzycki formulas, plus a table of training percentages to load your next session.
What is the One Rep Max Calculator?
A one rep max is the most weight you can move for one full repetition with good form. Coaches use it as a reference point: a program might call for 5 sets of 5 at 80% of 1RM, or a back-off set at 65%. Knowing your max (or a reliable estimate) turns those percentages into actual numbers on the bar. Because a genuine max attempt is fatiguing and raises injury risk, most lifters estimate it instead from a "rep max" they hit in normal training.
The estimate works because there is a fairly predictable relationship between the load you lift and the number of reps you can complete with it. Lift something you can only manage twice and you are close to your max; lift something you can do fifteen times and you are far from it. Rep-max equations capture this curve. The Epley formula, 1RM = weight x (1 + reps / 30), is one of the most common. The Brzycki formula, 1RM = weight x 36 / (37 - reps), is another widely used option. The two agree exactly at one rep and stay close through the low-rep range, then diverge as reps climb.
Accuracy is best when the set was genuinely hard, ideally taken to within a rep or two of failure, and when the rep count is low. Below about five reps the prediction is usually within a few percent of a tested max. Above ten or twelve reps, differences in conditioning, technique and which muscles fatigue first make any single formula much less reliable, so treat a high-rep estimate as a rough ballpark rather than a target to chase.
When to use it
- Setting training loads when your program prescribes a percentage of 1RM (for example 5x5 at 80%).
- Tracking strength progress over time without repeatedly testing a risky true max.
- Comparing the bench, squat and deadlift estimates to spot a lagging lift.
- Picking a sensible opening attempt for a powerlifting meet from recent gym sets.
- Checking whether a weight you can do for several reps is heavy enough to drive strength gains.
How to use the One Rep Max Calculator
- Enter the weight you lifted in a single set.
- Enter the number of clean reps you completed with that weight.
- Choose your unit, kilograms or pounds.
- Read your estimated 1RM from the Epley and Brzycki formulas, then use the percentage table to plan your working sets.
Formula & method
Worked examples
You bench press 100 kg for 5 clean reps and want your estimated 1RM.
- Epley: 1RM = 100 × (1 + 5 ÷ 30)
- = 100 × (1 + 0.16667) = 100 × 1.16667 = 116.7 kg
- Brzycki: 1RM = 100 × 36 ÷ (37 − 5)
- = 3600 ÷ 32 = 112.5 kg
Result: Estimated 1RM ≈ 116.7 kg (Epley) or 112.5 kg (Brzycki)
You squat 225 lb for 8 reps and want your estimated 1RM.
- Epley: 1RM = 225 × (1 + 8 ÷ 30)
- = 225 × (1 + 0.26667) = 225 × 1.26667 = 285.0 lb
- Brzycki: 1RM = 225 × 36 ÷ (37 − 8)
- = 8100 ÷ 29 = 279.3 lb
Result: Estimated 1RM ≈ 285.0 lb (Epley) or 279.3 lb (Brzycki)
Training percentages of a 116.7 kg estimated 1RM (from 100 kg x 5 reps, Epley)
| % of 1RM | Weight | Typical reps |
|---|---|---|
| 100% | 116.7 kg | 1 |
| 95% | 110.8 kg | 2 |
| 90% | 105.0 kg | 3 to 4 |
| 85% | 99.2 kg | 5 to 6 |
| 80% | 93.3 kg | 7 to 8 |
| 75% | 87.5 kg | 9 to 10 |
| 70% | 81.7 kg | 11 to 12 |
| 60% | 70.0 kg | 15+ |
Approximate reps-to-percentage guide used by rep max formulas
| Reps to failure | Approx. % of 1RM |
|---|---|
| 1 | 100% |
| 2 | 95% |
| 3 | 90% |
| 5 | 85% |
| 8 | 80% |
| 10 | 75% |
| 12 | 70% |
| 15 | 65% |
Common mistakes to avoid
- Estimating from a high-rep set. Rep max formulas are most accurate at one to five reps. Plug in a set of fifteen and the prediction can be off by a wide margin, because endurance and form breakdown play a larger role at high reps. Use your heaviest low-rep set when you can.
- Counting reps that were not clean. Half reps, bounced bench presses or a spotter quietly helping all inflate the rep count and overstate your max. Only count full-range repetitions you completed under your own power.
- Treating the estimate as a guaranteed lift. A predicted 1RM is a calculation, not a tested result. On the day, fatigue, sleep, nutrition and nerves all matter. Build up to any genuine max attempt gradually rather than jumping straight to the predicted number.
- Expecting the two formulas to match exactly. Epley and Brzycki agree at one rep and stay close at low reps, then drift apart as reps rise. The gap is normal: take the range between them as your working estimate rather than expecting a single exact figure.
Glossary
- One rep max (1RM)
- The maximum weight you can lift for a single full repetition of an exercise with good form.
- Rep max (RM)
- The most weight you can lift for a given number of reps, such as a 5RM (your best set of five).
- Epley formula
- A 1RM estimate: weight × (1 + reps ÷ 30), one of the most widely used rep max equations.
- Brzycki formula
- A 1RM estimate: weight × 36 ÷ (37 − reps), an alternative that tracks Epley closely at low reps.
- Working set
- A meaningful training set at a target load, often prescribed as a percentage of your 1RM.
- To failure
- Continuing a set until you cannot complete another rep with good form; rep max estimates are most accurate near this point.
Frequently asked questions
How do you calculate one rep max?
You estimate it from a set you have already done using a rep max formula. The Epley formula is 1RM = weight × (1 + reps ÷ 30), and the Brzycki formula is 1RM = weight × 36 ÷ (37 − reps). Enter the weight and reps from a hard set and this calculator applies both for you.
Which is more accurate, the Epley or Brzycki formula?
Neither is reliably better for everyone. They agree at one rep and stay very close through the low-rep range, then diverge as reps rise, with Epley tending to predict a slightly higher max at high reps. Most lifters use the range between the two as their estimate.
How many reps should I use for the best estimate?
Use a low-rep set, ideally one to five reps taken close to failure. Below five reps the prediction is usually within a few percent of a tested max. Above ten or twelve reps the estimate becomes much rougher and should be treated as a ballpark.
Is an estimated 1RM as accurate as testing it?
No. A formula gives a prediction, not a measured result. It is a safe, repeatable way to track progress and set training loads, but your actual max on the day depends on fatigue, technique, sleep and nerves. Build up gradually before attempting a true max.
How do I use the percentage table?
Most strength programs prescribe loads as a percentage of your 1RM. Find the percentage your program calls for, read the corresponding weight from the table, and load the bar. The typical reps column shows roughly how many reps that load usually allows.
How often should I retest or recalculate my 1RM?
Recalculating from your heaviest recent set every few weeks is enough for most lifters, since strength changes gradually. Testing a true 1RM is more demanding and is usually done only every few months or in the lead-up to a competition.
Sources
- Estimating One Repetition Maximum (1RM) , National Strength and Conditioning Association
- Predicting one repetition maximum equations accuracy , PubMed (U.S. National Library of Medicine)