Furniture Fit Checker 🛋️📏

The classic disaster: sofa bought online, delivery guys arrive, it doesn't make the corner at the top of the stairs — now you own a return-shipping nightmare. Or: desk fits the wall but blocks the door swing. This skill runs the geometry before money changes hands.

Overview

Three checks, one tool (scripts/fit_checker.py):

1. Path check — can the item pass a doorway/corridor/stairs? The moving-industry insight: a rigid box passes through an opening if it can be tilted diagonally. For a rectangular item (W×H×D) and a doorway (w×h), the effective clearance is the diagonal √(W²+D²) compared against the door width — plus corner-turning between corridor walls with the inner-diagonal trick. Handles:
   • doorway width vs item diagonal (item height vs door height)
   • L-shaped corner between corridors (inner-corner + outer-wall check)
   • straight staircase width vs diagonal, landing 180° turns
   • elevator cab diagonal (door + interior)
2. Room fit — does it fit where you want it, with walkways ≥ 30 in / 75 cm (interior-design standards: 75-90cm paths, 90+ around dining)? Checks wall-length fit, walkway to opposing furniture/door, door-swing clearance, and radiator/vent obstruction warnings.
3. Floorplan preview — ASCII render of the room with the furniture placed, so you can see the walkways before committing.

Everything in metric or imperial (auto-detected per value with explicit unit suffixes).

When to Use

• "Will this sofa (86×37×35 in) fit through my 32-inch door?"
• "Can a king mattress go up my staircase with a landing?"
• "Will the desk fit in the bedroom without blocking the closet door?"
• "Does the dining table leave room to pull chairs out?"
• Pre-purchase sanity check before ordering big furniture online
• Moving-day planning: order of items through each door

Don't use for: architectural planning (load bearing, code compliance), non-rectangular complex items (L-shaped sectionals — approximate as their bounding boxes per section), or piano moving (hire pros, seriously).

How It Works — Steps

1. Measure (a tape measure, 5 minutes): item W×D×H; door width × height (door open 90°, measure the frame minus trim); corridor widths if any; room dimensions; where you want it.
2. Path check:

   python3 scripts/fit_checker.py path --item 86x37x35in --door 32x80in
   

3. Corner / stairs if the route has them:

   python3 scripts/fit_checker.py corner --item 86x37x35in --hall-a 36in --hall-b 36in
   python3 scripts/fit_checker.py stairs --item 76x16x12in --width 36in --landing
   

4. Room fit:

   python3 scripts/fit_checker.py room --item 86x37in --room 14x11ft \
     --other 60x30in --floorplan
   

5. Look at the floorplan the tool prints; adjust and re-run.

The Geometry (exact rules)

1. Doorway: item passes iff item diagonal √(W²+D²) ≤ door width AND item min(W,D,H) ≤ door height (tilt through). Sofas: use arm-to-arm width and seat depth; add nothing — but if legs/arms removable, measure without them.
2. Corner (two corridors): moving trick — the item must satisfy inner diagonal check: for item length L and widths, at the critical angle θ where it simultaneously touches both outer walls and the inner corner: passes iff (L·sinθ + W·cosθ) ≤ min hall width for no θ... computed numerically over θ ∈ [0°, 90°] in 0.5° steps (exact for practical purposes).
3. Stairs: straight run — diagonal check vs stair width at the narrowest point (handrail, radiator, turn). With a 180° landing: the item must pivot on the landing; needs landing depth ≥ item diagonal × 0.75 (empirical moving rule; tight pivots need pros' experience).
4. Room walkways: distance from furniture edge to the nearest obstruction (wall, other furniture, door swing arc) ≥ 75cm/30in; dining-table chairs need +90cm/36in on chair sides.

Worked Example

Sofa 86×37×35in, door 32×80in:
  diagonal = √(86²+37²) = 93.6in > 32in → cannot pass flat
  BUT min(86,37,35)=35in... height check: 35in ≤ 80in ✓
  tilt geometry: sofa tilted on end, needs √(86²+35²)=92.9in vertical —
  exceeds 80in door height → FAIL flat-on-end
  workaround: angle-entry (two-person tilt) marginally possible —
  tool says TIGHT, remove door if hinge-pinned, or sofa legs off.

Common Pitfalls

1. Measuring the door slab, not the opening. A "34-inch door" is the slab; the clear opening with the door open 90° is ~2in less (trim, hinges). Measure the gap.
2. Forgetting the door swings IN. An entry door opening inward eats ~door-width of maneuvering room on the delivery side; remove the door (pop the hinge pins) for tight items.
3. Ignoring ceiling height on stairs. Low ceilings above stairwells (under stairs, sloped) block items that pass the width check — the minimum above-step clearance matters as much as width.
4. Using overall sofa dims when legs come off. 4in of legs = the difference between fail and pass. Always check removable feet first.
5. Hallway lights, radiators, baseboards narrow the nominal width by 2-6in at the critical point. Measure at the narrowest point, not the average.
6. Elevator: interior diagonal ≠ door diagonal. The cab is bigger than its door; the binding constraint is the door, then cab depth.
7. Box springs don't bend. A king mattress flexes around corners; a box spring/rigid base does not — that's what "split king" bases exist for.

Verification Checklist

• All measurements taken at the narrowest point of the path
• Door measured as clear opening (90° open, minus trim)
• Item height-vs-doorway-height check done, not just width diagonal
• Walkway check ≥ 75cm (30in) for every side you walk past
• Door-swing arcs drawn on the floorplan output
• Removable legs/arms measured without, noted in the decision

One-Shot Recipes

Online sofa listing sanity check:

python3 scripts/fit_checker.py path --item 213x94x89cm --door 81x203cm --report

Full route audit (door → hall → corner → stairs):

python3 scripts/fit_checker.py path --item 86x37x35in --door 32x80in
python3 scripts/fit_checker.py corner --item 86x37x35in --hall-a 40in --hall-b 36in
python3 scripts/fit_checker.py stairs --item 86x37x35in --width 36in --landing 36in

Will the bed + desk both fit?

python3 scripts/fit_checker.py room --item 60x80in --room 12x11ft \
  --other 48x24in --floorplan