One Rep Max Calculator

1. The Five Major 1RM Formulas

Every 1RM formula takes a sub-maximal weight and rep count and extrapolates to a theoretical max. They differ in mathematical model (linear, power-curve, exponential decay) and the populations they were validated against. Here is the full breakdown:

Where w is weight lifted and r is reps performed. Note that Mayhew uses the natural exponent constant e (~2.71828) and was developed specifically for the bench press.

2. Which Formula Is Most Accurate?

Comparative studies (LeSuer 1997, Mayhew 1992, Dohoney 2002) on trained populations show:

• Epley: ~3% mean error, most consistent across rep ranges 1-10. The safest default.
• Brzycki: ~3-5% mean error, slightly conservative. Best for low-rep testing (1-5).
• Lombardi: ~5% mean error, often overestimates at higher reps (8+).
• Mayhew: ~3% error for bench press specifically. Less accurate for squat/deadlift.
• O'Conner: ~4% error, conservative. NSCA-preferred for safety in programming.

The ToolWise calculator shows all five estimates plus the average. The "preferred formula" drives the training percentage table because programs like 5/3/1 and Starting Strength were designed around specific formula assumptions.

3. Why Reps Above 10 Are Unreliable

1RM formulas work well in the 1-10 rep range because the relationship between weight and reps is roughly linear-to-curved there. Above 10 reps:

• Form fatigue dominates — the limiting factor is no longer pure strength but muscular endurance and technique
• Cardiovascular limit sets in before muscular failure in some lifts
• Formulas diverge dramatically — at 15 reps, Epley and Brzycki can give 25%+ different estimates
• No validation data — most formula research stops at 10 reps because beyond that, the math becomes unreliable

If you need a max estimate from a 15-rep set, accept it as a rough ballpark (±15% error) rather than a precise number. For high-rep training, judge progress by rep performance rather than projected 1RM.

4. RPE vs Percentage Training

The training percentage table assumes that 80% of your 1RM equals a specific RPE on a specific day. In practice, daily readiness varies by ±5-10% based on:

• Sleep: One night of 5-hour sleep can reduce force output by 10-15%
• Nutrition: Glycogen depletion dramatically affects performance
• Stress: Cortisol and sympathetic nervous system state shifts
• Warm-up quality: A good warm-up can add 5% to working set performance
• Time of day: Strength peaks early evening for most people

Modern coaches (Mike Tuchscherer, Greg Nuckols, etc.) prescribe load by RPE rather than fixed percentage because it auto-corrects for daily readiness. The percentage table gives you a target; RPE gives you real-time adjustment.

5. Training Programs and Their Max Assumptions

Most beginners overestimate where they are in this progression. If you've been lifting less than a year and aren't yet stalling on linear gains, Starting Strength or StrongLifts is the right choice. Switch programs only when the current one stops working.

6. Peaking for Competition

A peaking protocol prepares the body to express maximum strength on a single day. The standard 8-12 week peaking block:

• Weeks 8-12 out (Accumulation): High volume, moderate intensity (70-80%), hypertrophy-focused accessories
• Weeks 4-8 out (Transmutation/Strength): Volume drops, intensity rises (80-90%), focus on competition lifts, doubles and triples
• Weeks 2-4 out (Intensification): Lower volume, high intensity (85-95%), singles and doubles with back-off sets
• Final 1-2 weeks (Taper/Peak): Volume drops 50-70%, intensity stays high (90-95%), only 2-3 singles per session
• Meet week: 2-3 days out, take a single at 80-85% to stay loose. Day before, rest completely. Day of, follow openers (90%) → second attempts (95%) → third attempts (100%+) as planned

7. Testing Protocol

When you do test a true 1RM, follow this protocol to maximize safety and accuracy:

• Warm up progressively: Empty bar → 50% → 70% → 80% → 90% of expected max, single reps each, 2-3 minutes rest
• Take 3-5 attempts, increasing by 2.5-5 kg each time
• 4-6 minutes rest between heavy attempts
• Have spotters and safety equipment — never squat or bench without them
• Stop at technical failure: form breakdown, not muscular failure. Grinding a miss rep teaches nothing
• Record attempts, not just successes — misses tell you where your ceiling is
• Wait 6-12 weeks before retesting. CNS recovery from max attempts takes longer than people think

8. Common Programming Mistakes

• Testing too often: max attempts tax the CNS for 1-2 weeks. Daily or weekly testing stalls progress
• Always working at the same percentage: the body adapts. Periodization (cycling intensity and volume) is required for ongoing gains
• Grinding every set: training to absolute failure is unnecessary and counterproductive on compounds
• Skipping warm-up sets: cold muscle injury is real. Always ramp up with progressive loads
• Comparing percentages across formulas: an Epley "85%" and a Brzycki "85%" are different absolute weights. Pick one formula and stick with it
• Ego lifting: lifting more than your form allows is the fastest path to injury. Numbers above technique = plateau + rehab

9. Privacy for Lift Data