One Rep Max (1RM) Calculator
Estimate your one-rep max from a submaximal set, using published strength-prediction formulas, plus a percentage-based training load table.
All Formula Estimates
No single formula is universally most accurate — the spread between them is a useful indicator of how much uncertainty to expect.
Training Load Percentages
Weights are calculated directly from your estimated 1RM. Typical rep counts for 100–70% are selected values from the NSCA training load chart; below 70% is commonly used for warm-up, technique or volume work where rep counts vary more.
One Rep Max (1RM) Calculator
Our One Rep Max Calculator estimates the heaviest weight you could lift for a single repetition, based on a set you’ve already performed with a lighter weight. Rather than relying on just one prediction method, it calculates all seven commonly used formulas — Epley, Brzycki, Lander, Lombardi, Mayhew, O’Connor and Wathan — and shows their average alongside a percentage-based training load table.
Why Estimate Your 1RM Instead of Testing It?
Testing a genuine one-rep max means working up to a single all-out lift, which carries a higher injury risk than regular training, especially without a spotter, safety equipment, or experience with maximal attempts. Estimating your 1RM from a submaximal set — for example, the heaviest weight you can lift cleanly for 3 to 6 reps — gives a useful working number for programming your training without that added risk.
The Seven 1RM Formulas
Each formula below takes the weight lifted (w) and the number of reps completed (r) and estimates your 1RM. They were developed from different research studies and don’t always agree — using several together, and looking at the spread between them, gives a more honest picture than trusting a single number.
| Formula | Equation | Notes |
|---|---|---|
| Epley (1985) | 1RM = w × (1 + r/30) | Simple and widely used; tends to run higher at higher rep counts. |
| Brzycki (1993) | 1RM = w × 36 / (37 − r) | Popular for the 1–10 rep range; becomes mathematically unstable as reps approach 37. |
| Lander (1985) | 1RM = 100w / (101.3 − 2.67123r) | Linear model, reasonable for moderate rep ranges. |
| Lombardi (1989) | 1RM = w × r0.10 | Power function; tends to run more conservative at higher reps. |
| Mayhew et al. (1992) | 1RM = 100w / (52.2 + 41.9e−0.055r) | Derived from bench press research specifically. |
| O’Connor et al. (1989) | 1RM = w × (1 + 0.025r) | Simple linear model adding a fixed 2.5% per rep; often among the more conservative estimates, particularly at higher rep counts. |
| Wathan (1994) | 1RM = 100w / (48.8 + 53.8e−0.075r) | Exponential model; often sits between the more aggressive and conservative estimates. |
How to Use the One Rep Max Calculator
- Choose your units — kilograms or pounds.
- Enter the weight you lifted and how many clean reps you completed with it.
- Optionally choose a specific formula, or leave it on the average of all seven.
- Click Calculate to see your estimated 1RM, the full spread across all seven formulas, and a training percentage table.
How Accurate Are 1RM Formulas?
Research comparing these formulas to actual tested maximums generally finds errors in the region of a few percent up to around 10%, with accuracy typically best for sets of around 2 to 10 reps performed close to failure. No single formula is consistently the most accurate across every rep range, exercise, or individual — beginners, isolation exercises, and very high rep counts (above roughly 12 to 15) all tend to reduce accuracy further. Treat any 1RM estimate as a useful planning figure rather than an exact number.
Training Load Percentages
Once you have an estimated 1RM, it’s common to plan training as a percentage of that number. The table below uses selected typical rep counts from the NSCA training load chart for 70–100% of 1RM; lighter percentages are generally used for warm-up sets, technique work, or higher-volume training where rep counts vary more by programme.
| % of 1RM | Typical Reps | Common Use |
|---|---|---|
| 100% | 1 | Maximal single |
| 95% | 2 | Near-maximal strength work |
| 90% | 4 | Heavy strength work |
| 85% | 6 | Strength work |
| 80% | 8 | Strength / hypertrophy |
| 75% | 10 | Hypertrophy |
| 70% | 12 | Hypertrophy / volume |
Rep counts are selected typical values from the NSCA training load chart, not a guarantee for any specific individual or exercise.
Frequently Asked Questions
Which 1RM formula is the most accurate?
No single formula is universally the most accurate — different studies, exercises, and populations produce different rankings, and no formula consistently outperforms the others in every situation. As a general pattern, accuracy tends to be better at lower rep counts performed close to failure and to decline as rep counts increase; individual factors like training experience, technique, and the specific exercise tested also affect how close any estimate lands to your true maximum. Using the average of several formulas, and treating the spread between them as your margin of uncertainty, is generally more informative than picking one formula and trusting it exactly.
How many reps should I use to estimate my 1RM?
Somewhere around 3 to 6 reps to (or close to) failure generally gives the most reliable estimate, since all the formulas were developed and validated mainly in that lower rep range. Estimates from sets above about 10 reps become progressively less reliable, and very high rep sets (15 or more) are not recommended for estimating a 1RM.
Is it safe to test my actual one-rep max?
Testing a true 1RM carries more injury risk than submaximal training, particularly without a spotter, safety equipment (such as safety bars or pins), a proper warm-up, and prior experience with maximal lifts. Many coaches recommend estimating 1RM from a submaximal set instead, especially for beginners, and only attempting a true maximal test under qualified supervision if at all.
Why do the formulas give different results for the same lift?
Each formula was developed from a different research study, often using a different population, exercise, or rep range, so they don’t always agree. The spread between formulas tends to widen at higher rep counts, which is one reason estimates from very high-rep sets are considered less reliable.
Do these formulas work for any exercise?
They were developed and validated mainly on compound barbell lifts such as the bench press, squat, and deadlift. They tend to be less reliable for isolation exercises, machine-based lifts, and exercises with a very different fatigue profile, so treat estimates for those movements with extra caution.
Should beginners use a 1RM calculator?
Yes, this is generally a safer approach than beginners attempting a true maximal lift, since submaximal-set estimation avoids the added risk of an all-out single attempt. That said, formula-based estimates for beginners can be less reliable, since inconsistent technique and unfamiliarity with true failure can affect the submaximal set used for the estimate.