Estimated 1RM Calculator

Title: Estimated 1RM Calculator Version: v1.0 QA status: PASS — full checklist run 2026-08-30 (functional, content, UX @320px/desktop, accessibility, print)

Purpose

Estimate a one-rep max from a submaximal set using three published formulas, and turn the estimate into practical percentage-based working loads — without requiring a true max attempt.

Intended user

Coaches and trainers prescribing percentage-based loading or tracking strength trends.

Inputs

• Load lifted (> 0, decimal allowed)
• Load unit: lb / kg
• Repetitions completed (integer 1–15)
• Bodyweight (optional, > 0) + bodyweight unit (lb / kg)

Outputs

• Epley, Brzycki, and Lombardi estimates
• Three-formula average
• Practical training 1RM (average rounded down to nearest 5 lb / 2.5 kg)
• Relative strength ratio (est. 1RM ÷ bodyweight, unit-normalized) when bodyweight given
• Working-load table 50–95% in 5% steps (exact + practical loads, typical programming zone)

Formulas

• Epley: 1RM = load × (1 + reps/30)
• Brzycki: 1RM = load × 36 / (37 − reps)
• Lombardi: 1RM = load × reps^0.10
• reps = 1 is special-cased: a completed maximal single is a measured 1RM (all formulas return the load, with an explanatory note).

Validation rules

• load > 0 else inline error; reps integer in [1, 15] else inline error; bodyweight blank or > 0
• No NaN/Infinity paths: results only render after all validations pass
• reps 7–10 → accuracy caution; reps 11–15 → strong reliability warning
• Bodyweight converted to load unit (1 kg = 2.2046 lb) before ratio

Assumptions

• Input set taken close to failure with consistent technique and full ROM
• Formulas are population averages validated mainly on barbell lifts
• Conservative rounding is intentional: percentages from an inflated max compound error

Limitations

• A calculated 1RM is not equivalent to a tested 1RM and is labeled as such in the UI
• Accuracy degrades with rep count; machine/unilateral/bodyweight movements transfer poorly
• Typical-use column describes common programming zones, not a prescription

Coaching application

Anchor percentage-based programming, set conservative testing-day openers, and track strength trends between formal tests. Guidance included on when estimation vs. direct testing is appropriate (coach's judgment; no medical claims).

Implementation notes

Single self-contained index.html (semantic HTML + embedded CSS/JS, no build step, no network dependency — Google Fonts load progressively with full system fallbacks). Formulas are pure named functions separated from formatting. aria-live results region, labeled controls, visible focus, keyboard operable (Enter calculates), print stylesheet renders results + methodology on white.