One-Rep Max Calculator
Calculate your one-rep max (1RM) from any weight and rep combination. Perfect for strength training, program design, and tracking progress.
Reviewed by the Calcura editorial team · Last reviewed
- Question
- How do I estimate my one-rep max (1RM)?
- Answer
- The Epley formula is the most common: 1RM = weight × (1 + reps / 30). 225 lb for 5 reps → 225 × (1 + 5/30) = 262.5 lb estimated 1RM. Brzycki is another option: 1RM = weight × 36 / (37 − reps), giving 253 lb for the same example. Accuracy is best in the 2–6 rep range. Above 10 reps, the formulas drift — use a lower-rep set for a cleaner estimate.
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- Formula
Epley: 1RM = weight × (1 + reps / 30)- Caveats
- Form degradation on maximal-effort reps inflates the predicted 1RM — stop at the last clean rep.
- Multi-joint lifts (squat, deadlift) predict more reliably than single-joint or machine lifts.
- Always test an actual 1RM under spotter supervision if you need a real number (competition, meet).
What This Calculator Does
This calculator estimates your one-repetition maximum (1RM) for a barbell lift based on any weight you can complete for multiple reps to failure or near-failure. You enter the load and the reps completed; the tool applies one of five published 1RM prediction formulas (Brzycki, Epley, Lombardi, Mayhew, O'Conner) and then projects percentage-based training weights from that estimate. It's a standard tool for program design — 5/3/1, Starting Strength, and most periodized templates use 1RM percentages to prescribe weights. Accuracy is best in the 2–6 rep range; above 10 reps the formulas diverge meaningfully and any single prediction should be treated as a rough ceiling rather than a precise figure.
When To Use This Calculator
Designing a strength block from a recent working set
You squatted 275 lb for 5 clean reps last week. Brzycki returns a 1RM of ~310 lb. An 85% Week 1 set (~265 lb) and 90% Week 2 set (~280 lb) becomes a reasonable starting progression — no need to risk a true max attempt.
Transitioning between rep ranges in a periodized plan
You ran a 10-rep hypertrophy block at 185 lb for bench press. Converting to strength work, 1RM ≈ 246 lb (Brzycki). For a 5×5 strength phase, 80% is ~197 lb — a meaningful jump from your old working weight but still in rep-able territory.
Comparing progress across a long training cycle
In March your 8-rep bench was 155 lb (1RM ≈ 191 lb). In September it's 175 lb for 8 (1RM ≈ 216 lb). That's ~13% estimated 1RM gain in 6 months — a reasonable trend line even without retesting a true max.
Coaching beginners who shouldn't test max singles
A first-year lifter who has done 95 lb × 5 on squat gets an estimated 1RM of ~107 lb. The coach can prescribe 75% sets (~80 lb) without asking them to attempt a potentially unsafe single-rep max.
How It Works
All 1RM formulas extrapolate from the reps-in-reserve / repetitions-to-failure relationship — as a lifter fatigues, they complete fewer reps at higher loads, and the relationship has been modeled empirically in several ways. Brzycki (1993) uses a linear fit: 1RM = load / (1.0278 − 0.0278 × reps). Epley is slightly more aggressive for low rep counts. Lombardi and Mayhew are nonlinear, handling higher rep counts better. O'Conner is a simple linear approximation. All assume a genuine reps-to-failure or near-failure effort; reps with significant reserve (RIR > 2) will underestimate true 1RM. Single-rep 1RM is also exercise-specific — a squat 1RM doesn't translate directly to leg-press strength.
Formula
Brzycki: 1RM = load / (1.0278 − 0.0278 × reps)
Epley: 1RM = load × (1 + reps / 30)
Lombardi: 1RM = load × reps^0.1Real-World Example
Scenario
Tomás, an intermediate lifter, deadlifts 365 lb × 4 with clean technique (last rep slightly sluggish but completed). He wants to set up training percentages for the next 8-week block.
Calculation
Brzycki: 365 / (1.0278 − 0.0278 × 4) = 365 / 0.9166 ≈ 398 lb Epley: 365 × (1 + 4/30) ≈ 414 lb Lombardi: 365 × 4^0.1 ≈ 418 lb Average across formulas: ~410 lb; conservative estimate (Brzycki) ≈ 398 lb
Result
Using the conservative ~398 lb estimate, Tomás can program 80% sets at ~320 lb, 85% at ~340 lb, and peak work around 90–92% (~360–365 lb) — weights he's genuinely rep-able with at current strength. If he tests a true max later in the block and hits 405 lb, the formulas called it within 2–5% of reality.
Common Mistakes to Avoid
Mistake: Applying 1RM formulas to high-rep sets
Solution: Prediction error grows sharply beyond 6–8 reps. A 20-rep set estimates 1RM well below your true max because endurance and conditioning limit the set, not pure strength. Use 2–6 rep sets as input when possible, or accept that a high-rep prediction is a rough floor.
Mistake: Treating estimated 1RM as a competition max
Solution: Estimated 1RM is calculated at gym conditions, with your own bar/plates and without competition singlets/commands. Powerlifting meets typically require a 5–10% discount to account for fatigue, depth/pause rules, and adrenaline effects — if you're programming for a meet, use a training max 90–95% of the estimate.
Mistake: Testing reps to failure every session
Solution: Regular failure training accumulates fatigue and impairs recovery. Use 1RM estimation from sets with 0–2 reps in reserve (RIR) rather than true failure, and estimate every 3–4 weeks, not weekly. The Epley/Brzycki curves are forgiving enough to tolerate slight RIR input.
Mistake: Using one formula for every lift
Solution: Brzycki tends to fit squat and bench well; deadlift and overhead press can skew differently due to leverages and fatigue patterns. For critical programming decisions, compute 2–3 formulas and take the median or conservative number rather than trusting a single prediction.
1RM Calculator vs. Related Strength Tools
BMI Calculator
Context for body weight relative to height — crude but useful when interpreting strength-to-weight ratios in categorization tables (e.g., strength standards by bodyweight).
Calorie Calculator
Pair with 1RM training to set a caloric surplus for strength gain or a maintenance intake during a peaking block where recovery matters most.
Macro Calculator
Protein is the primary lever for strength and muscle gain — 0.7–1.0 g/lb of body weight is typical. Use the macro calculator to translate a goal into daily grams.
When This Isn't the Right Tool
Novice lifters learning a new movement
Use instead: In the first 6–12 weeks of learning a lift, 1RM estimates are dominated by neural adaptation, not absolute strength. Prescribe sets by RPE (rate of perceived exertion) and add weight linearly session-to-session rather than using percentages.
Olympic lifts (snatch, clean & jerk)
Use instead: Power-based lifts depend on bar-speed and technique more than a max-strength rep range. Olympic weightlifting coaches use percentages of competition max but estimate them through a different progression — talk to a certified weightlifting coach.
Machine or isolation exercises
Use instead: Cable pulldowns, leg extensions, bicep curls, etc., don't follow the same reps-to-failure curve as compound barbell lifts. The formulas can over- or underestimate for these; program by RPE or rep ranges instead.
Rehab, return-to-sport, or injured populations
Use instead: Pushing close to true 1RM is contraindicated during rehabilitation. Work with a physical therapist or certified strength coach who can prescribe loading based on symptom response rather than maximum strength estimation.
How to Verify This Calculation
Cross-check two or three formulas on the same set. Brzycki and Epley should agree within 2–4% for sets of 3–6 reps. If they diverge >7%, your input reps probably had 2+ reps in reserve (suggesting the prediction underestimates), or the set was grindy past failure (suggesting it overestimates).
Sources
- Brzycki, M. (1993) — Strength testing equation — Original publication of the Brzycki formula in the Journal of Physical Education, Recreation & Dance.
- NSCA — Essentials of Strength Training and Conditioning — National Strength and Conditioning Association's flagship reference; covers 1RM estimation, percentage-based training, and periodization.
- ACSM — Resistance Training Guidelines — American College of Sports Medicine's position statements on resistance training load and volume prescription.
Reviewed by the Calcura editorial team · Last reviewed