Quick Answer: The most reliable test for loaded dice is the salt water flotation test — a fair die will rotate randomly in saturated salt water; a loaded die will consistently show the same heavy face downward. Statistical sampling (100+ rolls with chi-squared analysis) is the most scientifically rigorous method.
How Dice Are Loaded
A loaded die is one that has been deliberately manipulated to favor certain faces. Common methods include: filling one side with heavy material (wax, metal, lead weight) while leaving the opposite side lighter. Since dice rest with their heaviest face down, a die loaded on the face opposite "6" will favor landing on 6. Hollow dice with internal weights are harder to detect visually.
Test 1: The Salt Water Float Test
Dissolve as much salt as possible into warm water (creating a dense brine solution). Drop the die in and let it float freely. Rotate it gently and release. A fair die will come to rest at a different face each time. A loaded die will consistently rotate to show its lightest face upward (heaviest face down). Repeat 10-15 times — a pattern emerging indicates a loaded die.
Test 2: Statistical Roll Analysis
Roll the die 100+ times and record each result. Calculate the expected count (100 rolls ÷ 6 faces ≈ 16.67 per face). Apply a chi-squared test. If the test returns χ² > 11.07 (for 5 degrees of freedom and p < 0.05), the die is statistically biased. A 7% bias (rolling 6 ~23% vs expected ~17%) requires about 200 rolls to reliably detect.
Test 3: Visual and Physical Inspection
Check edges: are all edges equally sharp or are some corners more rounded? Measure face-to-face with calipers: a fair cubic die should be perfectly square. Look for internal modifications — some cheap dice have visible air bubbles or density variations visible through the plastic. Press on each face: a loaded die may have one face that feels slightly softer (wax fill) than others.