How much paint, hardener and reducer to buy for single-stage or base coat and clear coat. Every default is editable, because your product's tech sheet always wins.
Quantities are rounded up to whole quarts. Coverage varies with color, gun setup and how many coats you lay down, so check your product's technical data sheet.
The mixed amount is then split by the mix ratio into paint, hardener and reducer, and each is rounded up to whole quarts because that's how most paint is sold.
The coverage defaults (about 125 sq ft per gallon for single-stage and 150 to 160 for base coat and clear coat) follow Eastwood's published paint coverage guidance, which also recommends buying 10 to 20% extra. The vehicle areas are rough estimates for the outer skin. Mix ratios vary a lot between products, so set them from your product's technical data sheet.
Base coat provides the color and usually goes on with enough coats to hide the primer. Clear coat provides gloss and protection. Metallics and pearls often need an extra base coat for even coverage, so consider raising the waste figure for those colors.
Coverage guidance: Eastwood, "Calculating How Much Paint You'll Need to Paint Your Vehicle".