Your one-rep max (1RM) is the heaviest weight you can lift for a single perfect repetition — the anchor number for almost every serious strength programme. Bench 100 kg for 5 reps? Your true max is somewhere around 117 kg, and programmes like StrongLifts, nSuns, and Juggernaut need that number to set your working weights. Testing a true 1RM by loading the bar until you fail is slow, tiring, and risky — formulas like Epley’s estimate it from a submaximal set instead. Our free one rep max calculator uses the Epley formula to give your estimated 1RM plus a percentage table for training.
One Rep Max Calculator
Estimate your one-rep max from a working set (Epley formula).
The Epley Formula
Published in 1985 and still the gym standard:
1RM = weight × (1 + reps ÷ 30)
It works best for moderate rep ranges (2–10). At very high reps (12+), muscular endurance — not strength — skews the estimate, and other formulas (like Brzycki’s) drift closer. Under 10 reps, Epley is the trusted default.
| % of 1RM | Typical use | Approx. reps |
|---|---|---|
| 100% | True max | 1 |
| 95% | Near-max singles | 2 |
| 90% | Heavy strength work | 3–4 |
| 85% | Strength (5×5 territory) | 5–6 |
| 80% | Strength/hypertrophy | 7–8 |
| 75% | Hypertrophy | 9–10 |
| 70% | Volume work | 11–12 |
How to Use the One Rep Max Calculator
- Enter the weight you lifted (kg) and the reps you completed with good form.
- Click Calculate — your estimated 1RM and the percentage table appear.
- Programme from the percentages: 75–85% for building, 85–95% for peaking, and leave the true-max attempts for competition or test weeks.
Worked Example
Bench press 100 kg for 5 reps: 1RM = 100 × (1 + 5/30) = 100 × 1.1667 = 116.7 kg. Working weights: 85% ≈ 99 kg (5s), 75% ≈ 87.5 kg (10s). That’s exactly how a coach builds your plan.
Tips & Limitations
- Use a set that ended near failure with clean form — an easy 5 reps underestimates you.
- Estimates differ per lift: squat and deadlift follow formulas more reliably than bench; treat each lift’s estimate separately.
- Never attempt a true 1RM without a spotter/rack safeties; warm up in singles from ~80%.
- Beginners (under ~6 months) shouldn’t chase 1RMs at all — build technique at 60–80%.
Frequently Asked Questions
How accurate is the Epley formula?
Within a few percent for sets of 10 reps or fewer in trained lifters. It degrades at high reps because endurance becomes the limiter — that’s normal, and why coaches cap test sets around 5–8 reps.
Epley vs Brzycki — which is better?
Very close in the 2–10 rep range; Brzycki often edges it for lower reps (1–5), Epley for mid ranges. Consistency matters more — pick one and track progress with it.
What is a good 1RM?
Relative terms: a squat of 1.5× bodyweight, bench 1×, deadlift 2× are respectable trained milestones. Our FFMI calculator shows where your overall muscularity sits.
How often should I test my max?
Every 8–12 weeks is plenty. Most weeks, estimate from training sets — the calculator exists so you don’t have to max out to know.
Can I use it for machines or dumbbells?
Formulas were built on barbell lifts; machine/dumbbell numbers are less reliable (stabilisation and leverage differ). Use it as an estimate, not gospel.
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