One Rep Max Calculator — Free 1RM Strength Calculator | AllInOneTools
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One Rep Max Calculator

Estimate your one rep max using 7 proven formulas. Get training percentages, periodization chart, and rep-weight targets for strength, hypertrophy, and endurance.

lbs
reps
Estimated One Rep Max
263
lbs
average of 7 formulas • based on 225 × 5
📊 Formula Comparison
🏋 Training Percentage Chart

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One Rep Max: How to Estimate Your Maximum Strength Safely

Your one rep max (1RM) is the maximum weight you can lift for a single repetition with proper form. It is the gold standard for measuring absolute strength and the foundation for programming training percentages. Rather than risking injury by actually testing a true max, formulas allow you to accurately estimate your 1RM from a submaximal set of 2-10 reps.

The 1RM Formulas

Epley: 1RM = Weight × (1 + Reps/30)
Brzycki: 1RM = Weight × (36 / (37 - Reps))
Lander: 1RM = Weight × 100 / (101.3 - 2.67 × Reps)
Lombardi: 1RM = Weight × Reps^0.10
Mayhew: 1RM = Weight × 100 / (52.2 + 41.9 × e^(-0.055 × Reps))
O'Conner: 1RM = Weight × (1 + Reps/40)
Wathan: 1RM = Weight × 100 / (48.8 + 53.8 × e^(-0.075 × Reps))

Example: 225 lbs × 5 reps
Epley: 225 × 1.167 = 263 lbs
Brzycki: 225 × 1.125 = 253 lbs

Training with Percentages

Once you know your 1RM, you can program training weights with precision. Strength training uses 80-95% of 1RM for 1-5 reps per set. Hypertrophy (muscle growth) uses 65-80% for 6-12 reps. Muscular endurance uses 50-65% for 12-20+ reps. Periodization — systematically cycling through these intensity zones — prevents plateaus and optimizes long-term progress.

Accurate Estimation Tips
Use a 3-5 rep set for the most accurate estimate — accuracy drops significantly above 10 reps. Perform the test set when fresh (not pre-fatigued). Use strict form — cheating inflates the rep count and overestimates your max. Average multiple formulas for the best estimate. Recalculate every 4-8 weeks as you progress.
Safety Warnings
Never attempt a true 1RM without a competent spotter. Warm up thoroughly before heavy lifting: 5 minutes cardio, then sets at 40%, 60%, 80% of expected working weight. If your estimated 1RM seems unrealistically high (based on 10+ reps), use a lower-rep test set. Stop immediately if form breaks down or pain occurs. Beginners should train for at least 3-6 months before estimating or testing maximal strength.

Applying 1RM to Programming

A common 4-week periodization cycle: Week 1 at 70% for 4×8 (hypertrophy), Week 2 at 75% for 4×6, Week 3 at 80-85% for 5×4 (strength), Week 4 deload at 60% for 3×8 (recovery). This progressive overload ensures you train at appropriate intensities across rep ranges while allowing recovery. The percentages automate the guesswork — just plug in your 1RM and the training weights are defined.

Frequently Asked Questions

How is 1RM calculated? ▾
Epley: 1RM = Weight × (1 + Reps/30). Example: 225×5 = 263 lbs. Most accurate with 1-10 reps. Use multiple formulas and average for best estimate.
What is a good 1RM? ▾
Bench: Beginner 0.5×BW, Intermediate 1×BW, Advanced 1.5×BW. Squat: Beginner 0.75×, Intermediate 1.25×, Advanced 2×BW. Varies by age, gender, training history.
Which 1RM formula is best? ▾
Epley and Brzycki are most validated. Nearly identical for 1-6 reps. Averaging all 7 formulas gives the best overall estimate. Accuracy decreases above 10 reps.
Should I test actual 1RM? ▾
A calculated estimate from 3-5 reps is safer and nearly as accurate. If testing: use spotter, warm up thoroughly, max 3 singles. Beginners should avoid true 1RM testing.
What % of 1RM for training? ▾
Strength: 80-95% for 1-5 reps. Hypertrophy: 65-80% for 6-12 reps. Endurance: 50-65% for 12-20 reps. Deload: 40-60%.
How often to recalculate? ▾
Every 4-8 weeks during training cycles. Recalculate when you hit a new rep PR. Progressive overload means 1RM should gradually increase over time.