Length vs area confusion
Converting ft to m is not the same as ft² to m² — you must square the conversion factor for area.
Volume vs weight in cooking
ml is volume while grams are weight; only equal for water at specific conditions. Use proper density or stick to one system.
Temperature formulas
Use °F = °C × 9/5 + 32 and °C = (°F − 32) × 5/9 — not a simple ratio.