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Fitness & Weight
One Rep Max Calculator — Estimate Your 1RM (Epley & Brzycki)
Turn any weight-and-reps set into an estimated 1RM and a ready-to-use percentage chart
Your one-rep max (1RM) is the most weight you can lift for a single, full repetition of an exercise — think bench press, squat, deadlift or overhead press. It's the number coaches use to set up training programs, because almost every percentage-based plan (5/3/1, Starting Strength, most powerlifting peaks) is written as a percentage of your max. The problem: actually testing a true 1RM is risky, tiring and not something you want to do every week. That's where an estimate comes in.
This calculator predicts your 1RM from a set you already did — a weight you lifted for a known number of reps. Two well-known formulas do the work. Epley: 1RM = weight × (1 + reps ÷ 30). Brzycki: 1RM = weight × 36 ÷ (37 − reps). Both are research-backed and land within a few pounds of each other in the useful range.
Worked example. You bench 225 lb for 5 reps. Epley gives 225 × (1 + 5 ÷ 30) = 225 × 1.1667 = 262.5 lb. Brzycki gives 225 × 36 ÷ (37 − 5) = 8100 ÷ 32 = 253.1 lb. So your estimated max is roughly 253–263 lb — call it about 260. From there the percentage table tells you that your 5-rep working sets (around 85%) sit near 220 lb, and a heavy single attempt (95%) is around 250 lb.
The common mistake: trusting the estimate at high reps. These formulas are most accurate from 1 to about 10 reps. Plug in a set of 20 and the math will badly overestimate your max — endurance sets just don't predict a true single. For the cleanest number, use a hard set of 3 to 8 reps left close to failure.
A percentage chart (95/90/85/80/75/70/65/60%) turns that single max into a full menu of training loads, each with a typical rep range so you know whether a weight is meant for heavy triples or higher-rep volume work.
This is an informational estimate, not medical or coaching advice. Real maxes vary by exercise, fatigue, technique and the day. Always warm up, use a spotter or safeties on big lifts, and round to the plates you actually have. If you have any injury or health concern, talk to a qualified trainer or physician before maxing out.
📖 See also: How to Calculate a Tip (and Split the Bill)
Calculator
Fill in the fields and click "Calculate" for instant results.
📰 Formula
• Epley: 1RM = weight × (1 + reps / 30) • Brzycki: 1RM = weight × 36 / (37 − reps) • Training load at P%: load = 1RM × (P / 100) • Best accuracy at 1–10 reps; estimates drift high above ~12 reps
📰 Formula
• Epley: 1RM = weight × (1 + reps / 30) • Brzycki: 1RM = weight × 36 / (37 − reps) • Training load at P%: load = 1RM × (P / 100) • Best accuracy at 1–10 reps; estimates drift high above ~12 reps
🧪 Worked examples
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Example 2
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Example 3
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Example 4
⚠️ Common mistakes
- Using a high-rep set (15–20+). Above ~12 reps the formula overestimates your true 1RM.
- Entering total reps across several sets instead of reps in one continuous set.
- Treating the estimate as an exact max — it's a prediction, not a guarantee for the day.
- Maxing or testing without warming up, a spotter, or safety pins on heavy lifts.
💡 Tips
- For the most reliable estimate, use a hard set of 3–8 reps taken close to failure.
- Re-estimate every few weeks from your working sets instead of testing a true single often.
- Round results to the plates you own (usually the nearest 5 lb) and start lighter when in doubt.
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❓ Frequently asked questions
What is a one rep max (1RM)?
Your one rep max is the most weight you can lift for a single full repetition of an exercise with good form. Programs often prescribe weights as a percentage of this number.
How does this one rep max calculator work?
Enter a weight you lifted and how many reps you did in one set. It applies the Epley and Brzycki formulas to estimate the single-rep max, then builds a percentage table of training loads.
Which is more accurate, Epley or Brzycki?
Both are reliable from about 1 to 10 reps and usually agree within a few pounds. Epley tends to read slightly higher at higher reps. Using both gives you a sensible estimate range rather than one fragile number.
How many reps should I use for the best estimate?
A hard set of 3 to 8 reps taken close to failure gives the most reliable estimate. Avoid sets of 15 or more — the math overestimates your true max at high reps.
Why are my Epley and Brzycki numbers different?
They're two different equations fit to real lifting data, so they diverge a little — more so as reps climb. The gap is normal; treat the two values as the low and high end of an estimate.
Is it safe to actually test my 1RM?
Testing a true single is demanding and carries injury risk. Warm up thoroughly, use a spotter or safety pins on bench, squat and press, and stop if form breaks down. Many lifters just estimate from working sets instead.
What percentage of my 1RM should I train at?
It depends on the goal: roughly 85–95% for strength and low-rep work, 70–85% for hypertrophy volume, and 60–70% for higher-rep or technique work. The table on this page lists typical rep ranges for each percentage.
Does this work for bench, squat and deadlift?
Yes. The formulas apply to any standard barbell lift. Just remember each lift has its own 1RM — your squat estimate doesn't transfer to your bench.
Is this calculator medical or coaching advice?
No. It's an informational estimate. Real maxes vary with fatigue, technique and the day, and the formulas are predictions. Consult a qualified trainer or physician before maxing out, especially with any injury or health concern.