The three formulas used
| Method | Formula | Practical behaviour |
|---|---|---|
| Epley | weight × (1 + reps ÷ 30) | Often produces a slightly higher estimate at lower repetition counts. |
| Brzycki | weight × 36 ÷ (37 − reps) | Rises more steeply as repetitions approach the formula's upper practical range. |
| Lombardi | weight × reps0.10 | Uses a power relationship and may sit above or below the other methods depending on the set. |
For a genuine single repetition, ToolBullet returns the entered load for all three methods. The calculator accepts up to 15 repetitions but marks sets above 10 as lower confidence because endurance, pacing and proximity to failure increasingly influence the result.
Example: 100 kg for five repetitions
Epley: 100 × (1 + 5 ÷ 30) = 116.7 kg.
Brzycki: 100 × 36 ÷ 32 = 112.5 kg.
Lombardi: 100 × 50.10 ≈ 117.5 kg.
ToolBullet comparison average: about 115.6 kg, with a spread of about 5.0 kg.
The spread shows model uncertainty. It is more honest to plan around a band than to claim that 115.6 kg is a measured fact. Repeating the same exercise and technique under similar conditions makes the trend more useful.
Choosing a useful input set
- Use the same exercise, equipment, range of motion and technique you want to track.
- Enter a completed set whose repetition count is known and technically consistent.
- Avoid using a set stopped far from fatigue unless the result is deliberately treated as a conservative lower estimate.
- Do not compare machine, dumbbell and barbell estimates as though they were interchangeable.
Using percentage loads
Percentage tables help convert the estimate into repeatable training targets. If the comparison average is 115.6 kg, 80% is 92.5 kg after sensible plate rounding. The exact training load still depends on the exercise, programme, experience and how the athlete is performing that day. Current ACSM guidance emphasises individualisation and consistency rather than a single universally perfect loading scheme.
Compare the three estimates in the One-Rep Max Calculator. The selected percentage can be passed privately in the same tab to the Plate Calculator; lifted weight is not placed in a share URL.
What the estimate cannot tell you
An equation cannot evaluate bracing, spotting, injury history, technique breakdown, fatigue, sleep, pain or whether a maximal attempt is appropriate. Studies of predictive equations show that validity depends on the population, lift and testing method. Treat the output as a programming and trend tool—not permission to attempt the displayed number.
Tracking the estimate over time
A single estimate is less useful than a consistent series. Record the exercise, load, repetitions, equipment and any material change in technique. Compare like with like: a paused bench press should not silently replace a touch-and-go benchmark, and a machine setting should remain documented. A rising estimate across several technically comparable sessions is stronger evidence of progress than one unusually good set. If the formulas spread farther apart at higher repetitions, use the lower end or repeat the assessment with fewer repetitions rather than reporting false precision.
How it works and sources
Method and sources reviewed 7 July 2026. ToolBullet uses these sources to explain the method and its limits; it does not replace coaching, medical advice or official governing-body records.