One-Rep Max (1RM) Calculator
Inputs
| Weight Lifted | 100 kg |
|---|---|
| Reps Completed | 5 |
| Formula | Epley |
Visualization
| Reps Completed | Weight Lifted (kg) |
|---|---|
| % of 1RM | Weight Lifted (kg) |
|---|---|
One-Rep Max (1RM) Calculator
Estimate your one-rep maximum from a sub-maximal lift using common strength-training formulas (Epley, Brzycki, Lombardi, O'Conner, Wathen).
Inputs
Lift Performed
Results
Enter a value to see results.
Lifting 100 kg for 5 reps gives an estimated one-rep max of ....
Predicted Weight by Reps
| Reps Completed | Weight Lifted (kg) |
|---|---|
Training Percentages
| % of 1RM | Weight Lifted (kg) |
|---|---|
Estimating a Max Without Maxing Out
In strength training, the one-rep max (1RM) is the heaviest weight you can lift exactly once with proper form. It's the standard benchmark for prescribing training loads — most programs reference percentages of 1RM ("3 × 5 at 80% of 1RM"). The catch: actually testing 1RM is risky and exhausting. A failed max attempt under heavy load is the most common path to a serious lifting injury.
The workaround is estimation from a sub-maximal lift. Lift a weight you can do for 5–10 reps, then plug into a formula. Several formulas exist; this calculator implements the five most-cited ones (Epley, Brzycki, Lombardi, O'Conner, Wathen) and lets you compare.
How It Works
Every formula takes the same two inputs — weight lifted, reps completed — and returns an estimated 1RM. They differ in the curve they fit through historical data:
| Formula | Equation | Notes |
|---|---|---|
| Epley | $w(1 + r/30)$ | Most cited; published 1985. Linear correction. |
| Brzycki | 1993; common in barbell training literature. Hyperbolic. | |
| Lombardi | Power-curve fit; tends to underestimate for high reps. | |
| O'Conner | Linear; tends to overestimate vs. observed. | |
| Wathen | Exponential; fits a wider range of reps. |
For 1 rep, all formulas correctly return . They diverge as grows — at 10 reps, the spread between formulas can be ±5–8%. Reps 3–6 give the tightest agreement between formulas; treat that as the most reliable input range.
Training-Percentage Reference
Most programs prescribe loads as percentages of 1RM:
| % of 1RM | Reps possible | Training intent |
|---|---|---|
| 100% | 1 | Maximal effort |
| 95% | 2 | Heavy single |
| 90% | 3–4 | Strength |
| 85% | 5 | Strength |
| 80% | 6–8 | Strength / hypertrophy bridge |
| 75% | 8–10 | Hypertrophy |
| 65–70% | 10–15 | Hypertrophy / volume |
| < 60% | 15+ | Endurance / form work |
The reps-possible numbers are approximate and depend on the lift (squats and deadlifts often allow more reps at a given % than bench press) and on the lifter's training age. The calculator also shows a rep-count table — the predicted weight for 1 through 10 reps — so you can read your working load straight off the row for the rep target you are programming.
Practical Scenarios
1. Programming Your Next Cycle
You bench 100 kg for 5 reps. Epley estimates 1RM at 116.7 kg, Brzycki at 112.5 kg. A conservative program target would round down: take 110 kg as your working 1RM, then 80% of that (88 kg) for your 5 × 5 strength sets. You bench 225 lb for 5 reps. Epley estimates 1RM at 262.5 lb, Brzycki at 253.1 lb. A conservative program target would round down: take 250 lb as your working 1RM, then 80% of that (200 lb) for your 5 × 5 strength sets.
2. Tracking Strength Progress
Estimate 1RM from your top working set every few weeks. Trends are more useful than single readings — formula error largely cancels when comparing your own estimates over time.
3. Comparing Lifters
Bench-press 1RM as a percentage of bodyweight is a common informal benchmark (1 × bodyweight bench is "intermediate," 1.5 × is "advanced"). Estimating from a multi-rep set is the safer path to that comparison.
4. Returning From Layoff
After a few weeks off, do not retest 1RM directly. Pick a moderate weight, hit 5 honest reps, and let the formula tell you where you stand. Conservative programs use 90% of the estimate as the working number for the first re-build cycle.
Where the Formulas Fall Short
- Very high reps mislead. All these formulas assume the rep set is taken close to muscular failure. A "10 reps with 5 left in the tank" set produces a meaningless estimate. Train to within 1–2 reps of failure for reliable inputs.
- Different lifts, different curves. The original studies fit data from bench press primarily. Squats and deadlifts often show steeper curves (you can do relatively more reps at high percentages), and bench shows shallower curves. Brzycki tends to be conservative for squats; Epley reads about right for bench; both diverge for deadlifts.
- Trained vs. untrained. Formulas were validated mostly on trained lifters. A novice may complete more reps at a given % of true 1RM than these tables suggest.
- Don't actually test 1RM unsupervised. The formulas exist to avoid maxing out. If you do test, do it with a spotter, in a safety rack, after a thorough warm-up. Form failure under heavy load is the most common serious-injury vector in lifting.
Frequently Asked Questions (FAQ)
Which formula should I trust?
For 3–6 reps, all five formulas agree to within about 2–3%. Epley is the most cited and a fine default. Brzycki tends to be slightly more conservative; O'Conner slightly higher. For best estimates, use a 3–6 rep set and average the formulas if you want one number.
Why is the estimate unreliable for high-rep sets?
Above ~10 reps, the relationship between reps and percentage-of-1RM becomes increasingly noisy. Endurance and pacing become limiting factors, not pure strength. Sub-maximal sets used for estimation should be hard — within 1–2 reps of failure — and ideally between 3 and 6 reps.
Do these formulas work for all lifts equally?
Not exactly. They were originally validated mostly for the bench press. Squats and deadlifts tend to show shallower drops (more reps possible at a given % of true 1RM), so estimates from multi-rep deadlift sets may understate true 1RM slightly. Treat the calculator output as a baseline and adjust based on your own testing.
Should I actually test my 1RM?
For most recreational lifters, the answer is "rarely." Form breakdown under maximal load is the leading cause of lifting injuries. Estimating from a 5RM set gives 95%+ of the useful information for programming. If you do test, do it with a spotter, in a power rack with safety pins, after a thorough warm-up — and ideally in a meet, where the conditions and judging make it worth the risk.
Disclaimer
1RM estimates assume the input set was taken close to muscular failure with proper form. They are not medical or coaching advice; consult a qualified strength coach for individualized training. Lifting heavy weights carries injury risk — train within your ability and use spotters or safety equipment for max-effort attempts.