Each vehicle is materialized as a constrained 3D solid and then partitioned into discrete cargo zones — trunk, fold-flat deck, individual rear seats, footwells, front passenger seat, and (for trucks) a divided cab and bed. Zones are generated dynamically from the year/make/model dimensional record, then reshaped against the live passenger layout: an occupied seat removes its zone, an empty middle seat yields a partial footwell penalized by an OEM-sourced transmission-tunnel height, and a folded rear bench produces both a stackable cargo deck and an under-deck footwell layer.

The solver uses a high-resolution height-map approximation of the well-known 3D Bin Packing Problem (NP-hard, formalized by Martello, Pisinger & Vigo, 2000). Items are sorted by physical volume and placed in priority order (cargo → footwell → seat); every item is evaluated in all six axis-aligned orientations and assigned the lowest valid landing position consistent with width, depth, and the applicable headrest-limited ceiling. The result is a placement that is physically achievable in the real vehicle — not merely volumetrically plausible.

Tall items (height > 18") are programmatically barred from passenger-seat placement to prevent forward sight-line obstruction and braking-projectile hazards. Folded-bench loading is automatically suppressed when the rear row carries two or more passengers. Stacked cargo is bounded by the lowest applicable headrest line — front-row for solo drivers, rear-row otherwise — preserving rearward visibility.

Each item carries an industry-standard weight pulled from TSA / IATA / major-carrier baggage policy and Home Depot retail product weight ranges. Carry-on luggage is modeled at 35 lb and a standard checked bag at 50 lb (the per-bag threshold above which most US carriers assess overweight fees). Moving-box weights track the realistic upper end of typical packed loads. Total payload is summed live from your loadout and itemized below the headline figure.

Base highway MPG is sourced from EPA fueleconomy.gov and averaged across the published range for each model and generation. Fuel-tank capacity is resolved from a sub-class lookup (Compact Sedan, Midsize Sedan, Compact / Midsize / 3-Row SUV, Full-Size Truck) calibrated against published OEM specifications. The weight penalty applies the US Department of Energy fuel-economy guideline — roughly 1% per 100 lb in conventional vehicles, with a conservative 1.5% / 100 lb coefficient used here to reflect highway-cruise aerodynamic and rolling-resistance effects. Adjusted range = adjusted MPG × tank capacity.

A 500-mile reference trip is priced against the AAA-published US average for regular gasoline ($3.50/gal default). Empty cost uses base MPG; loaded cost uses penalty-adjusted MPG. The "Penalty" cell isolates the marginal dollar cost attributable to the current load — useful for sanity-checking whether a heavy haul is worth the round trip.