Epley
1RM = W × (1 + R ÷ 30)
100 kg × 5: 100 × (1 + 5 ÷ 30) = 116.7 kg.
Linear rep adjustment; divergence grows as repetitions rise.
One Rep Max Calculator (1RM) — Estimate Your Maximum
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Percentage loads
Loads will be based on your estimated 1RM. Repetition ranges are broad reference points, not prescriptions.
| Percentage | Approximate reps | Calculated load |
|---|---|---|
| 100% | 1 | — kg |
| 97.5% | 1–2 | — kg |
| 95% | 1–2 | — kg |
| 92.5% | 1–3 | — kg |
| 90% | 1–3 | — kg |
| 87.5% | 2–4 | — kg |
| 85% | 2–5 | — kg |
| 82.5% | 3–6 | — kg |
| 80% | 3–6 | — kg |
| 77.5% | 4–8 | — kg |
| 75% | 5–8 | — kg |
| 72.5% | 6–10 | — kg |
| 70% | 6–10 | — kg |
| 67.5% | 8–12 | — kg |
| 65% | 8–12 | — kg |
| 62.5% | 10–15 | — kg |
| 60% | 10–15 | — kg |
| 57.5% | 12–20 | — kg |
| 55% | 12–20+ | — kg |
| 52.5% | 15–25+ | — kg |
| 50% | 15–25+ | — kg |
Using the table: higher percentages are commonly used for strength practice, moderate percentages can support hypertrophy work, and lower percentages can support technique or endurance work. Actual repetitions vary widely by exercise, tempo, rest, training background, and proximity to failure.
Plate-loading helper
Inventory uses denomination:quantity pairs, where quantity is the number of plates available per side. The solver checks all permitted combinations and chooses the closest total load.
| Target | Goal | Achievable | Difference | Plates per side |
|---|---|---|---|---|
| Calculate a 1RM to see plate plans. | ||||
Choose and interpret your input set
How to choose a set
Use a recent set from the exact exercise you want to estimate. The repetitions should use consistent range of motion and technique, and the set should finish close to technical failure—the point where another repetition would require a meaningful breakdown in form. Sets of roughly 2–10 repetitions are generally more useful than long, highly fatiguing sets.
Estimated versus tested 1RM
An estimated 1RM predicts a maximum from a submaximal set. A tested 1RM is a load actually completed once. The estimate is usually more convenient for routine programming, but it is not a promise that the predicted load can be lifted today. A bench press estimate applies only to that bench press variation; do not transfer it to a squat, deadlift, machine, or different range of motion.
How to interpret formula differences
A narrow formula range means the three mathematical models happen to agree for that input. A wide range signals more model uncertainty, not a personal confidence interval. Use the same formula and similar set conditions when tracking change over time.
When not to test a true maximum
Do not attempt an unfamiliar maximal lift when technique is inconsistent, you are injured or unwell, equipment or safeties are unsuitable, or qualified help is needed but unavailable. Beginners can build strength effectively from submaximal loads without testing a true 1RM.
Calculation methodology
In the equations below, W is the lifted weight and R is effective repetitions (completed reps plus RIR when enabled). For a single repetition, this calculator returns W directly. Otherwise it calculates all three estimates and uses their median as the default: the middle value after sorting them. This prevents one extreme formula from pulling the answer up or down, but it has not been proven universally superior. You can select an individual formula in Advanced options.
Brzycki
1RM = W ÷ (1.0278 − 0.0278 × R)
100 kg × 5: 100 ÷ (1.0278 − 0.139) = 112.5 kg.
The denominator becomes increasingly sensitive at high repetitions, so this page limits entry to 20.
Lombardi
1RM = W × R0.10
100 kg × 5: 100 × 50.10 = 117.5 kg.
A power model. It may be higher or lower than other formulas; it is not assumed to be better for high-repetition sets.
Fully worked example: 100 kg × 5 reps
Epley gives 116.7 kg, Brzycki gives 112.5 kg, and Lombardi gives 117.5 kg. Sorted, those results are 112.5, 116.7, and 117.5 kg, so the default median estimate is 116.7 kg. The formula spread is 112.5–117.5 kg. At 80%, the unrounded training load is 93.3 kg.
Why estimates diverge
The equations impose different curve shapes on the relationship between repetitions and load. Real strength-endurance also varies by exercise and person, so technique, muscle groups, training background, tempo, and whether the set was truly near failure can matter more as repetitions increase.
Sources
- Mayhew et al. (1995), muscular-endurance equations for bench press — found prediction errors varied and reported Brzycki as most accurate in that sample for sets of 10 or fewer.
- Reynolds, Gordon & Robergs (2006), prediction from multiple-repetition testing — reported better prediction accuracy from 5RM than 10RM or 20RM data in bench press and leg press.
- Richens & Cleather (2014), training background and reps at percentages of 1RM — illustrates why percentage-to-repetition charts cannot be universal.
Author: Starlight Robotics. Last reviewed: 19 July 2026. No independent strength-professional review is claimed.
One Rep Max Calculator FAQ
How many reps should I use for a 1RM estimate?
Use a recent hard set of about 2–10 repetitions. Lower-repetition sets close to technical failure generally provide a more useful estimate than high-repetition sets.
Does the set need to reach failure?
No. Stop at technical failure or just before it. If you deliberately stopped early, enter your estimated reps in reserve so the calculator can use completed reps plus RIR.
Why do 1RM formulas disagree?
Each equation models the relationship between load and repetitions differently and was developed from different data. The gap usually grows as repetitions increase.
What happens if I enter one repetition?
The calculator returns the weight lifted as the estimated 1RM because a successful hard single is already a one-repetition result.
What is the difference between estimated and true 1RM?
An estimated 1RM is predicted from a submaximal set. A true or tested 1RM is the heaviest load actually completed once under the same technique and equipment conditions.
Is 1RM exercise-specific?
Yes. A bench press estimate applies to that bench press variation, not to a squat, deadlift, dumbbell press, or another movement.
How does RIR affect the estimate?
RIR means reps in reserve. The calculator adds RIR to completed reps to approximate repetitions possible at failure; larger values also reduce the confidence label.
How should I use percentage loads?
Use them as starting points for programming, then adjust for the lift, goal, fatigue, and individual response. The displayed repetition ranges are approximate, not prescriptions.
Should beginners test a true 1RM?
Usually an estimated 1RM from a controlled hard set is more practical while technique is developing. Seek qualified supervision before attempting an unfamiliar maximal lift.