How the one rep max calculator works
Your one-rep max (1RM) is the heaviest weight you can lift for a single repetition with proper form. This calculator estimates it from a sub-maximal set — enter the weight you lifted and how many reps you completed, and it predicts what your true maximum would be using three established formulas.
The projection table and chart show how much weight you should be able to handle at every rep count from 1 to 20, making it easy to program training loads without guessing.
How to use it
- Enter the weight you lifted and select kg or lbs.
- Enter how many reps you completed with good form (1–10).
- Read your estimated 1RM from three formulas (Epley, Brzycki, Lombardi).
- Use the projection table to find your working weights at any rep range.
How the formulas work
Three formulas estimate your 1RM from different mathematical models:
The Epley formula is used as the primary result and to generate the projection table. It is linear (each additional rep adds weight/30 to the estimate), which makes it intuitive and widely applicable.
Why three formulas are shown
No formula is perfect for everyone. Showing all three gives you a confidence range:
- Epley — linear, widely used, works well for 3–10 reps. Tends to slightly overestimate at very high reps.
- Brzycki — ratio-based, very similar to Epley at low reps but diverges above 7–8 reps. Popular in academic research.
- Lombardi — exponential, tends to give slightly higher estimates across all rep ranges. Best for experienced lifters.
When the three formulas agree closely (within 2–3%), you can be confident in the estimate. When they diverge, use the middle value.
How to read the projection table
The table shows two perspectives on your strength:
Reps → Weight: for each rep count (1–20), the maximum weight you should be able to handle. Use this to pick working weights for your program.
% of 1RM → Reps: for each intensity percentage, the expected weight and how many reps you should get. Use this to translate percentage-based programs into actual loads.
How to use percentages for training
Different percentage ranges target different adaptations:
| % of 1RM | Reps | Training goal |
|---|---|---|
| 90–100% | 1–3 | Maximal strength, neural adaptations |
| 80–90% | 3–6 | Strength with some hypertrophy |
| 70–80% | 6–12 | Hypertrophy (muscle growth) |
| 60–70% | 12–20 | Muscular endurance |
| 50–60% | 15–30 | Speed work, warm-up sets, recovery |
Most programs use 70–85% for the bulk of working sets. Deload weeks drop to 50–65%.
Getting the most accurate estimate
The prediction is only as good as the input set. Follow these guidelines:
- Use 3–5 reps for the most accurate prediction. The formulas were validated in this range.
- Go to near-failure. If you could have done 2 more reps, the set was 7 reps at the listed weight, not 5. Honest effort produces honest estimates.
- Use compound barbell lifts. The formulas work best for squat, bench, deadlift, and overhead press. Isolation exercises and machines have different fatigue curves.
- Rest fully before the test set. Fatigue from prior sets reduces the weight you can handle, skewing the estimate low.
Common mistakes to avoid
- Counting sloppy reps. If form broke down on the last 2 reps, don't count them. The formula assumes quality reps where the muscle, not momentum, did the work.
- Using more than 10 reps. Above 10, endurance becomes the limiting factor rather than raw strength. The prediction becomes unreliable.
- Applying the estimate to different exercises. Your bench press 1RM does not predict your overhead press 1RM. Test each lift independently.
- Not recalculating. Your 1RM changes as you get stronger. Recalculate every 4–6 weeks to keep training loads progressive.
- Attempting a true 1RM unnecessarily. For most people, an estimated 1RM is sufficient for programming. True max attempts carry injury risk and require proper warm-up, spotters, and recovery.
Limitations
These formulas are population averages. Individual factors like fiber type distribution (fast-twitch vs slow-twitch dominance), training age, exercise selection, and fatigue management affect the actual relationship between sub-maximal reps and true max. Some lifters can grind out more reps at a given percentage than others. Use the estimate as a starting point and adjust based on how the prescribed weights actually move in training.
Frequently asked questions
Which 1RM formula is the most accurate?
No single formula is universally best. Epley and Brzycki are the most widely cited and tend to be most accurate in the 3–7 rep range. Lombardi works well across a broader range but can overestimate at very low reps. Using multiple formulas gives you a realistic range rather than false precision.
Why do the formulas give different numbers?
Each formula was developed from different study populations and uses a different mathematical model. Epley is linear (weight × (1 + reps/30)), Brzycki uses a ratio (weight × 36/(37−reps)), and Lombardi uses an exponent (weight × reps^0.1). At low reps they agree closely; at higher reps they diverge more.
Why is the rep range limited to 1–10?
1RM predictions become significantly less accurate above 10 reps because muscular endurance and fatigue tolerance introduce too much variability. A 10-rep set tests endurance as much as raw strength. For the most reliable estimates, use a weight you can lift for 3–5 reps with good form.
How do I use the percentage table for training?
The percentage table translates your 1RM into working loads. For maximal strength, use 85–95% (1–5 reps). For strength-hypertrophy, 75–85% (5–8 reps). For hypertrophy, 65–75% (8–12 reps). For muscular endurance, 50–65% (12+ reps). These are starting points; adjust based on how the weight moves.
Should I test my actual 1RM or use an estimate?
For most recreational lifters, an estimated 1RM from a 3–5 rep set is safer and sufficient for programming. True 1RM testing carries injury risk and requires proper warm-up, spotters, and recovery time. Competitive powerlifters test true maxes with proper peaking protocols before competition.
How often should I recalculate my 1RM?
Recalculate every 4–6 weeks or at the end of a training block. Strength adaptations accumulate over weeks, so testing more frequently just reflects daily variation in readiness. Use the updated 1RM to adjust training loads for the next mesocycle.
Does this work for all exercises?
These formulas were validated primarily on compound barbell lifts (squat, bench press, deadlift, overhead press). They work reasonably for most resistance exercises but may be less accurate for isolation movements, machine exercises, or bodyweight exercises due to different fatigue and leverage patterns.