Calculator · 1RM Calculator
Estimate 1RM: what might my maximum be?
The 1RM calculator estimates your one-repetition maximum from a multi-repetition set. It deliberately displays two equations so the result is understood as a model value rather than a directly measured maximum.
Result
- Estimated 1RM (Epley)
- 117.5kg
- 100 %
- 117.5kg
- 95 %
- 110kg
- 90 %
- 105kg
- 85 %
- 100kg
- 80 %
- 92.5kg
- 75 %
- 87.5kg
- 70 %
- 82.5kg
- 65 %
- 75kg
- 60 %
- 70kg
Brzycki comparison: 112.5 kg. Different equations can produce different estimates.
Model range ≈ 1 reps
Model range ≈ 2 reps
Model range ≈ 3–4 reps
Model range ≈ 5–6 reps
Model range ≈ 7–8 reps
Model range ≈ 9–10 reps
Model range ≈ 11–12 reps
Model range ≈ 13–15 reps
Model range ≈ 16–20 reps
Treat the result as an estimate. For programming, a repeatable method is more useful than a supposedly perfect single number.
Method
How the calculation works
The primary value uses Epley: weight × (1 + repetitions/30). The calculator also computes Brzycki: weight × 36 / (37 − repetitions). The percentage table is based on the rounded Epley estimate.
Percentage-table weights are rounded to 2.5 kg. The attached repetition ranges are practical model ranges and are not individually derived from your strength-endurance profile.
Methodology: formulas, assumptions and estimate confidence →
Estimate confidence
How reliable is this estimate?
Medium
1RM equations are useful approximations, but accuracy depends on the lift, person and repetition count. Uncertainty is especially high above 10 repetitions.
Interpretation
How to read your result
Use the result as an approximation for programming and tracking. If Epley and Brzycki differ, that is useful evidence that the input does not have one objectively exact extrapolated answer.
For percentage-based programming, consistency is often more useful than false precision: same exercise, similar technique and comparable set conditions make changes over time easier to interpret.
Limits
Where this calculator ends
Prediction equations can differ in accuracy by exercise, training status, repetition count and individual. A blanket claim such as 'within ±5–10 % for everyone' would therefore be misleading.
Uncertainty generally rises at higher repetition counts. A true 1RM is a separate performance test and should only be attempted with suitable technique, preparation and safety measures.
Common mistakes
Common mistakes
- 01Reading one decimal place as real measurement precision.
- 02Using a set far above ten repetitions for a precise max extrapolation.
- 03Ignoring equation differences and selecting only the highest estimate.
- 04Treating the generic percentage/repetition mapping as an individual profile.
- 05Attempting the estimated 1RM directly without a progressive build-up.
Example
A worked example
5 repetitions at 100 kg
Epley: 100 × (1 + 5/30) ≈ 116.7 kg, then rounded to the calculator's 2.5 kg step. The page shows that model estimate and Brzycki for comparison. Derived percentage weights are programming anchors, not prediction guarantees.
FAQ
Frequently asked questions
- How does the calculator estimate my 1RM?
- Primarily with Epley and additionally with Brzycki. Both derive an estimate from weight and repetition count; neither directly measures your actual maximum.
- How accurate is the estimate?
- There is no single error margin for every person and lift. Accuracy depends on the equation, exercise, repetition count, technique and training status.
- How many repetitions should I use?
- Lower repetition counts are generally more suitable for 1RM extrapolation. The calculator explicitly warns above 10 repetitions because uncertainty increases.
- What do the reps beside the percentage table mean?
- They are generic orientation ranges. The weights are percentages of your Epley estimate; your actual repetitions at those weights can differ.
- Do I need to test a real 1RM?
- No. A consistently used estimate is enough for many programming decisions. A true max test is only necessary if you specifically need to measure that performance and can do so appropriately.
Sources
Sources
- 01Brzycki M. Strength Testing—Predicting a One-Rep Max from Reps-to-Fatigue. Journal of Physical Education, Recreation & Dance. 1993;64(1):88–90. The Brzycki equation is a prediction equation, not a direct 1RM measurement.
- 02Mayhew JL, Prinster JL, Ware JS, Zimmer DL, Arabas JR, Bemben MG. Muscular endurance repetitions to predict bench press strength in men of different training levels. Journal of Sports Medicine and Physical Fitness. 1995;35(2):108–113. Prediction accuracy varied by equation and repetition range; lower-repetition tests were generally more useful.
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