Strength
One-Rep Max Calculator
Estimate one-rep max with Epley, Brzycki, and Lombardi formulas.
Result
Loading table
Loads rounded to the nearest 2.5 kg.
| % of 1RM | Load | Reps to failure |
|---|---|---|
| 100% | 115 kg | 1 |
| 95% | 110 kg | 1–2 |
| 90% | 105 kg | 3–4 |
| 85% | 97.5 kg | 4–6 |
| 80% | 92.5 kg | 6–8 |
| 75% | 87.5 kg | 8–10 |
| 70% | 80 kg | 10–12 |
| 65% | 75 kg | 12–15 |
| 60% | 70 kg | 15–20 |
| 50% | 57.5 kg | 20+ |
Formula comparison
Six formulas show the likely range of your true 1RM.
Formula from LeSuer 1RM-equation comparison (1997) and Brzycki (1993), checked against the source on May 25, 2026.
What does the One-Rep Max Calculator calculate, and which formula does it use?
The One-Rep Max Calculator estimates your 1RM from a submaximal set using six published formulas — Epley (w × (1 + r/30)), Brzycki (w × 36/(37 − r)), Lombardi, Mayhew, Wathen, and Lander — then averages all six, builds a 50–100% loading table (rounded to 2.5 kg or 5 lb) with approximate reps to failure, and derives the 90% training max used by percentage-based programs like 5/3/1.
Last updated .
How far off can this be?
In 70 adults tested at 1, 5, 10 and 20 reps, even a prediction equation fitted to their own 5-rep sets estimated the bench-press 1RM with a standard error of 2.98 kg and the leg-press 1RM with 16.16 kg, and accuracy fell as reps rose; the authors advise no more than 10 reps in a linear equation.
For the example set (100 kg for 5 reps on the bench), the six formulas this calculator runs give 112.5 kg to 119.0 kg, an average of 116.0 kg. Treat the spread between formulas as the least the estimate can be off by, not the most.
The standard errors come from one sample's own fitted equation, so a general formula on a different lifter will usually miss by more. Sets of 10 reps or fewer keep the estimate tighter.
Source: Reynolds, Gordon & Robergs 2006, J Strength Cond Res, “Prediction of one repetition maximum strength from multiple repetition maximum testing and anthropometry” .
How to use it
- Enter the weight you lifted and the number of reps completed in your best recent working set. This calculator compares six validated estimation formulas: the Epley formula (1RM = weight x (1 + reps/30)), the Brzycki formula (1RM = weight x 36 / (37 - reps)), and the Lombardi formula (1RM = weight x reps^0.10), plus the Mayhew, Wathen, and Lander equations. Each formula was derived from different study populations and performs differently across rep ranges. The Epley formula, published by Boyd Epley at the University of Nebraska in 1985, remains the most widely used in strength training literature. All six formulas are most accurate between 2 and 10 reps; at 5 reps they sit within about 6% of each other (100 kg × 5 gives 112.5 to 119 kg). Beyond 10 reps the estimates spread further because muscular endurance starts to shape the set more than peak strength. For the most reliable estimate, use a weight you can lift for 3-6 reps with good form and full range of motion.
- Use the loading table under the result to turn your estimated 1RM into working weights (switch Units to US for pounds; loads round to 2.5 kg or 5 lb). Hypertrophy training typically uses 65-75% of 1RM for sets of 8-12 reps, strength training uses 80-87% for sets of 3-5 reps, and maximal strength peaking uses 90-100% for singles, doubles, and triples. For example, if your estimated bench press 1RM is 100 kg, your hypertrophy working sets would use 65-75 kg, strength sets would use 80-87 kg, and peak sets would use 90-100 kg. Keep loads above about 90% for experienced lifters with spotters or safety pins. For most training purposes, an estimated 1RM is safer and more practical than a true tested maximum, because actual 1RM attempts carry meaningful injury risk, especially on compound lifts like squats and deadlifts.
- When you have estimates from multiple rep counts, compare them to identify accuracy. A 5-rep set and a 3-rep set should produce 1RM estimates within 3-5% of each other if both were performed at true maximal effort. If your 10-rep estimate is significantly higher than your 3-rep estimate, the higher-rep set likely was not taken to true failure, or your endurance exceeds your peak strength relative to population averages. In that case, trust the lower-rep estimate because it is closer to the actual neuromuscular output the 1RM represents. Reynolds, Gordon and Robergs (2006, Journal of Strength and Conditioning Research) likewise found 1RM predicted more accurately from a 5-rep max than from 10- or 20-rep maxes. The formula chart and spread show how much the six formulas disagree for your set.
- Track your estimated 1RM over successive training blocks to measure real progress. A 3-5% increase in estimated 1RM over a 4-6 week training block represents solid progress for intermediate lifters who have been training consistently for 1-3 years. Beginners in their first year of training can expect 5-10% gains per block on compound movements due to rapid neuromuscular adaptation. Advanced lifters with 5+ years of training may see only 1-2% improvements per block, and progress is better measured across 12-16 week macrocycles. If your estimated 1RM is stagnant across two consecutive blocks, your programming likely needs a stimulus change such as variation in rep scheme, tempo, or exercise selection.
- Re-test your working sets every 4-6 weeks at the end of a training block. Use the same exercise variation, same range of motion, and similar conditions each time for valid comparison. Do not compare a paused bench press 1RM estimate to a touch-and-go estimate, and do not compare a high-bar squat estimate to a low-bar estimate. The difference between variations can be 5-15% and will mask real progress. If you train using RPE-based programming, your RPE 10 set at a given rep count provides the input needed here without requiring a separate test session. Many coaches in the Reactive Training Systems methodology developed by Mike Tuchscherer use this approach to track 1RM trends without the fatigue cost and injury risk of dedicated max-out sessions.
Questions people usually ask
What formulas does this calculator use and how do they differ?
This calculator compares six validated formulas: Epley (1RM = weight x (1 + reps/30)), Brzycki (1RM = weight x 36 / (37 - reps)), and Lombardi (1RM = weight x reps^0.10), plus the Mayhew, Wathen, and Lander equations. The Epley formula, published by Boyd Epley at the University of Nebraska in 1985, is the most widely cited in strength training literature. Brzycki gives lower estimates than Epley below 10 reps; the two meet at exactly 10 reps and Brzycki runs higher above it. Lombardi uses a power curve (reps^0.10) rather than a straight line, so it gives the lowest estimates at high reps. At 5 reps the six formulas sit within about 6% of each other and they spread further past 10 reps. The calculator presents all six and their average so you can see the range and lean on the lower estimates for safety.
How accurate are 1RM estimates compared to actual tested maximums?
Accuracy depends most on the rep count. Reynolds, Gordon and Robergs (2006, Journal of Strength and Conditioning Research) found a 5-rep max predicted the tested 1RM more accurately than 10- or 20-rep maxes. Past 10 reps, muscular endurance shapes the set more than peak strength, so the estimate gets looser. For the most reliable estimate, use a recent set of 3-5 reps taken close to failure with good form.
Should I actually test my one-rep max in the gym?
For most training purposes, an estimated 1RM is safer and more practical than a true tested maximum. Actual 1RM attempts carry meaningful injury risk, particularly on compound lifts like squats and deadlifts, and produce significant central nervous system fatigue that can impair training for several days afterward. The NSCA recommends that only experienced lifters with spotters and proper equipment attempt true 1RM testing. For programming purposes, an estimated 1RM derived from a 3-5 rep set provides sufficient accuracy to set training loads.
Why does my estimated 1RM differ between exercises?
Different exercises have different rep-to-max relationships based on muscle groups involved and movement patterns. Isolation exercises and machine movements tend to allow more reps at a given percentage of 1RM than compound barbell movements. Deadlifts often produce lower rep-to-max ratios than squats because grip fatigue and spinal loading accumulate faster. The formulas were primarily validated on compound barbell movements, so they are most accurate for squat, bench press, deadlift, and overhead press.
How often should I update my estimated 1RM?
Re-estimate every 4-6 weeks, usually at the end of a training block before starting the next. Progress per block shrinks as your training age rises. If your estimated 1RM has not moved across two consecutive blocks (8-12 weeks), look at volume, intensity, exercise selection or recovery.
What is the difference between a training max and a true 1RM?
A training max is typically set at 85-90% of your estimated true 1RM and is used as the reference point for calculating working weights in many popular programs like 5/3/1 by Jim Wendler. Using a training max instead of a true 1RM provides a built-in buffer that reduces injury risk and allows for productive training even on suboptimal days. If your estimated 1RM is 150 kg, your training max at 90% would be 135 kg, and your working sets would be calculated from that lower number.
Does the formula account for body weight or training experience?
No. The Epley, Brzycki, and Lombardi formulas are purely mathematical relationships between weight lifted and reps completed. They do not account for body weight, training age, sex, or exercise type, and individual lifters can sit well above or below the curve (endurance-dominant lifters manage more reps at a given percentage). For bodyweight-relative strength comparison, use the result in the Strength Percentile Calculator.
Can I use Smith machine or machine exercise numbers?
You can, but the estimate only applies to that machine. Smith machines and other machines change stability demands, bar path and friction, so a machine max and a free-weight max can differ by a meaningful margin in either direction, depending on the lift and the machine. Use this calculator with the exercise variation you actually train and program for.
Is this tool free and private to use?
Yes. AI Fit Hub tools are free, no-signup browser tools. All calculations run locally in your browser and no data is sent to any server.
The formula, worked through
- Formula RPE to Percentage Formula (Tuchscherer)
RPE to percentage formula: the Tuchscherer (RTS) chart maps reps × RPE to a share of 1RM; RPE 8 for 5 reps is 81.1%. Worked squat example and the RIR scale.
The same numbers as a table
- Reference One-rep max by reps and weight lifted
Computed by this calculator's engine across common inputs, to cite or download as CSV.
- Benchmark 2026 one-rep-max formula disagreement benchmark
Computed by this calculator's engine across common inputs, to cite or download as CSV.
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Background on the One-Rep Max Calculator
- Guide How to Use Your One-Rep Max for Training Programming
How to use your one-rep max for programming: estimate it from a 3-5 rep set, set a training max at 85-90%, load sets by percentage, and adjust with RPE.
- Statistics One-Rep Max Statistics: Strength Standards by Lift
One-rep max statistics: squat, bench and deadlift norms from 809,986 drug-tested powerlifting entries, 1RM formula accuracy and strength loss with age.
- Statistics Strength Training Statistics: Health & Mortality Data
Strength training statistics: participation, mortality reduction, volume, frequency and failure research, and health effects, each with its source.
- Statistics Gym Membership Statistics: US Trends and Demographics
Gym membership statistics from the Health & Fitness Association (formerly IHRSA): US member counts, growth and demographics, each with its source.
- Statistics Home Gym Statistics: Adoption, Outcomes, & Equipment
Home gym statistics: how band, bodyweight and home-based training compare with gym training, home rehabilitation results and what keeps people training.
- Statistics Periodization Statistics: Block, Linear & Undulating Models
Periodization statistics from meta-analyses: periodized vs non-periodized, linear vs undulating and block models, volume, frequency, deloads and tapering.
Articles
- 11 min read Training to Failure vs Reps in Reserve: What Works
Training to failure vs reps in reserve, reviewed: Robinson 2024 recasts the binary debate as a continuous proximity curve where size and strength diverge.
- 11 min read Light vs Heavy Weights for Muscle Growth: The Evidence
Light vs heavy load for muscle growth: the Schoenfeld 2017 meta, Morton 2016, and Lasevicius 2018 show similar hypertrophy to failure, load wins 1RM.
- 15 min read Evidence-Based Hypertrophy Program: Sets, Reps, Frequency
Evidence-based hypertrophy program: 10-20 hard sets per muscle a week, 30-85% 1RM near failure, frequency to spread volume, per Pelland 2026 and Schoenfeld.
By goal
Use it from an agent or code
Any agent can run this calculator by URL: put the inputs in the query string and get JSON back, with the inputs that used defaults and a line to cite (add format=md for markdown). MCP clients reach it through https://aifithub.io/mcp.
In code, import the same module; it runs where you import it, with no request or key.
import { compute } from "https://aifithub.io/engines/one-rep-max-calculator.js";Input and output contract, TypeScript types and the guide for agents.