How We Calculate

Every fit verdict starts with a 3D bounding-box comparison. We model items and spaces as rectangular solids, then test whether the item clears the constraint in any of its 6 possible orientations (the three axes, each with two rotation permutations).

For each orientation we check length, width, and height against the space's clear opening — accounting for real-world factors like door trim depth, stair landing turning radius, and elevator door width vs. cab interior width.

We apply clearance tolerances based on the constraint type. Doorways use a 0.5-inch tolerance for frame variation. Stairs apply a 1-inch margin to account for railing protrusion. Elevators compare both the door opening and the cab interior separately, since the door is almost always the tighter constraint.

The result is one of five verdicts: Fits, Tight Fit, Fits if Tilted, Doesn't Fit, or Fits — Won't Close (for containers with lids or doors that can't shut around the item).

Our Data Sources

Standard dimensions for doors, hallways, stairs, and elevators come from the building codes published by the International Code Council (ICC) — specifically the IRC (residential) and IBC (commercial) code families.

Accessibility dimensions reference the ADA Standards for Accessible Design and the ANSI A117.1 standard for accessible buildings and facilities.

Elevator safety and capacity data references the ASME A17.1 Safety Code for Elevators and Escalators.

Furniture dimensions are sourced from manufacturer specifications and industry data (e.g., ISPA for mattress sizes). We verify against multiple retailers and round to the most common marketed dimensions.

Standards We Reference

Code	Description	Source
IRC R311.2	Egress door minimum clear width (32 in.)	View
IRC R311.6	Hallways — minimum width 36 in.	View
IRC R311.7	Stairway width, headroom, and riser/tread dimensions	View
IBC Chapter 10	Means of egress — commercial corridor and door widths	View
ADA 404	Accessible doorways — maneuvering clearance and opening force	View
ADA 403	Accessible routes — minimum clear width and passing space	View
ADA 407	Elevator accessibility — cab size, door width, and controls	View
ASME A17.1	Safety Code for Elevators and Escalators	View
ANSI A117.1	Accessible and Usable Buildings and Facilities	View

How the AI Calculator Works

The interactive calculator uses our proprietary AI extraction pipeline to parse natural-language descriptions of your item and space. When you type "my couch is 84 inches long and 35 inches deep," the model extracts structured dimensions and passes them to our constraint solver.

The constraint solver is a deterministic algorithm — not a language model prediction. It tests all 6 rotation permutations of the item against the space's clear opening, applies tolerance margins specific to the constraint type (door, stair, elevator, vehicle), and returns one of five verdicts: Fits, Tight Fit, Fits if Tilted, Doesn't Fit, or Fits — Won't Close.

The AI handles conversation and dimension extraction. The math is handled by code with no randomness — the same inputs always produce the same verdict.

Data Freshness Policy

Standard dimensions are reviewed whenever new code editions are published. The current reference editions are the 2021 IRC, 2021 IBC, 2010 ADA Standards, and ASME A17.1-2019.

Furniture and appliance dimensions are updated quarterly against manufacturer catalogs and retailer listings. When a product category changes significantly (e.g., a new standard mattress size gains market share), we update our defaults within 30 days.

Vehicle cargo dimensions are refreshed annually when new model-year specifications are released by manufacturers. We prioritize the most commonly searched vehicles first.

Transparency

ItemFits does not use fabricated reviews, fake testimonials, or inflated ratings. We do not add AggregateRating schema markup because we have not collected sufficient verified user ratings to do so honestly.

Every fit verdict is generated algorithmically from the dimensions you provide. There is no editorial override — the math determines the result.

Our standard dimension data is updated when building codes are revised. The current reference editions are the 2021 IRC, 2021 IBC, 2010 ADA Standards, and ASME A17.1-2019. We cite code sections on every calculator page that uses them.