Your one-rep max (1RM) is the most weight you can lift for a single repetition with good form. Rather than testing it directly — which is risky and needs a spotter — this calculator estimates it from a set you have already done. Enter the weight and reps, and it averages two of the most widely used formulas for a reliable figure, then builds a table of training weights.
The two formulas and why they differ
Both formulas were derived from research on weightlifters and are widely used in strength training programs:
Epley (1985): 1RM = weight × (1 + reps ÷ 30)
This formula is linear in reps and tends to estimate slightly higher than
Brzycki at higher rep counts. It has no mathematical breakdown at any rep count.
Brzycki (1993): 1RM = weight × 36 ÷ (37 − reps)
This formula uses a hyperbolic relationship and tends to be slightly more
conservative. It approaches infinity as reps approach 37, so it is only
valid for sets well under 37 reps — practically speaking, accuracy degrades
beyond about 15 reps.
The average of the two reduces the bias of either formula alone and is a common approach used in strength programming. For sets of 1–5 reps, both formulas are quite close; they diverge more at higher rep counts.
How it works
The tool computes two established 1RM estimates and averages them:
- Epley:
1RM = weight × (1 + reps ÷ 30) - Brzycki:
1RM = weight × 36 ÷ (37 − reps)
The headline figure is (Epley + Brzycki) ÷ 2. It accepts 1–30 reps but is most
accurate at 10 reps or fewer. From the estimated max it then derives target
weights using standard percentages of 1RM (for example 87% for a 5-rep set).
Worked example
You bench press 100 kg for 5 reps:
- Epley:
100 × (1 + 5/30) = 116.7 kg - Brzycki:
100 × 36 ÷ (37 − 5) = 112.5 kg - Estimated 1RM (average): approximately 114.6 kg
| Reps | % of 1RM | Target weight |
|---|---|---|
| 1 | 100% | 114.6 kg |
| 3 | 90% | 103.1 kg |
| 5 | 87% | 99.7 kg |
| 8 | 80% | 91.6 kg |
| 12 | 70% | 80.2 kg |
How to use the training percentage table
Different rep ranges and intensities serve different training goals. Common programming uses these percentages as a guide:
- 90–100% (1–3 reps): Near-maximal strength; builds absolute strength but requires more recovery. Used in peaking blocks before competition.
- 80–87% (4–6 reps): Strength-focused hypertrophy range — the “sweet spot” for combining strength gains with muscle growth.
- 70–80% (6–10 reps): Classic hypertrophy range; most commonly used for building muscle mass.
- 60–70% (10–15 reps): Muscular endurance and lighter volume work; useful for deload weeks or accessory lifts.
If your program prescribes “4 sets of 5 at 87% of 1RM” and your estimated max
from this calculator is 114.6 kg, your target working weight is approximately
114.6 × 0.87 ≈ 99.7 kg. Round to the nearest available plate increment.
Why not just test your true 1RM?
Testing a true maximum is appropriate for competitive powerlifters and experienced athletes before a competition. For most lifters, it carries unnecessary risk (muscle strain, joint stress) and requires a qualified spotter. Estimating from a quality set of 3–6 reps — where you stop with good form and about 1–2 reps left in the tank — gives a reliable figure with far less risk.
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