Compare bar sizes on the metric that a simple price-per-gram calculation misses: how much you actually pay for each gram of contained fine gold.
Size efficiency is the relationship between the money paid and the fine-gold quantity obtained. The result normalizes bars of different weights so they can be compared on an equivalent basis.
Larger bars often have different retail premiums, but the actual relationship depends on the product and seller. Enter the real prices you are considering instead of assuming that a particular size always has the lowest premium.
A low acquisition cost per fine gram is useful for comparing purchases, but resale liquidity and dealer buyback spreads are separate questions.
Purchase price divided by the actual grams of pure gold contained in the bar.
Yes. Fine-gold normalization makes the comparison possible.
No. It identifies the lowest entered acquisition cost per fine gram.