Methodology
How We Calculate Fit
Real car interiors are irregular shapes, not perfect rectangular boxes. This page explains exactly what our calculator does, and — just as importantly — what it doesn't do.
1. Normalize every dimension to millimetres
Whatever unit you enter (mm, cm, m, inches or feet), we convert it directly to millimetres using exact conversion factors (1in = 25.4mm, 1ft = 304.8mm) before any comparison. We never chain unit-to-unit conversions, which avoids compounding rounding error.
2. Test all six orthogonal orientations
A rectangular object with edges L × W × H can be presented to the vehicle six different ways (L×W×H, L×H×W, W×L×H, W×H×L, H×L×W, H×W×L). We evaluate every one against the vehicle's opening and cargo geometry and select the best-performing orientation — we never conclude an item 'is too wide' without checking whether turning it solves the problem.
3. Check the boot opening separately from the cargo space
These are different constraints. An item's cross-section (the two dimensions perpendicular to the direction of travel) must clear the boot opening width and height. Independently, its footprint must fit within the cargo width, height and depth once inside. A vehicle can have a huge cargo volume and still fail on a narrow opening — this is why FitTheLoad never uses cargo volume (litres) alone to answer 'will it fit'.
4. Prefer the wheel-arch-limited width when we have it
Many SUVs and hatchbacks are wider overall than the usable gap between the rear wheel arches. When we have a verified between-wheel-arches figure, we use it as the binding cargo width, since that's the real constraint for a rigid object.
5. Compare seats up vs seats folded
Where we have a verified cargo depth for both configurations, we calculate a full result for each and show a side-by-side comparison, so you can see whether folding the seats is what makes the difference.
6. Apply a clearance margin
A raw dimensional pass (object slightly smaller than the opening) doesn't account for trim, hinges, upholstery, protrusions or measurement error in the real world. You can choose Exact Dimensions (0mm), Standard Estimate (25mm per constrained dimension) or Conservative Estimate (40mm). A result under the margin but still technically positive is shown as 'Very Tight Fit', not a comfortable pass.
7. Classify data completeness before answering
If a required vehicle measurement is missing (null, not estimated), the corresponding check is marked 'unknown' rather than silently passing or failing. A verdict is downgraded to 'Possibly Fits' rather than a false 'Likely to Fit' whenever a key dimension hasn't been verified.
8. Produce an explainable confidence level
Confidence (High / Medium / Limited) is based on how many of the five key dimensions are verified, the strength of their provenance (manufacturer > technical source > reliable secondary source > owner measurement), and whether the calculated clearance is comfortably above the chosen margin. We show the specific reason for the confidence level — never a fabricated percentage like '97% fit probability'.
What we deliberately don't do
- We don't model arbitrary-angle (diagonal) loading. Whether tilting an object in 3D lets it pass through a smaller opening is a genuinely hard geometry problem that depends on details we don't have (exact interior shape, obstructions, room to maneuver). Where a close-call failure might plausibly be solved by tilting the item, we show a "Diagonal fit may be possible" note — but we don't claim to calculate it precisely, and you should verify manually.
- We don't invent vehicle measurements. If a figure hasn't been verified from a manufacturer page or a named, reputable source, it's left blank — never estimated from a photo, a different trim, a different model year, or the vehicle's general size class.
- We don't solve multi-item packing. Checking a single item at a time is what V1 does well. Fitting ten different boxes together efficiently is a separate, much harder optimization problem we haven't built yet.
- We don't check weight against payload capacity yet. Payload includes occupants, fuel and other cargo, and figures aren't exposed for most vehicles in our current dataset — this is on the roadmap.
Result language, explained
- Likely to Fit
- Every relevant dimension is verified and clears your chosen margin in at least one orientation.
- Very Tight Fit
- It technically clears in the best orientation, but by less than your chosen margin — small real-world differences could change the outcome.
- Possibly Fits
- At least one relevant dimension isn't verified for this vehicle, so we can't confirm the result reliably.
- Unlikely to Fit
- At least one verified dimension is smaller than the item in every orientation tested, though a diagonal approach might help.
- Does Not Fit Based on These Dimensions
- The item is larger than a verified vehicle measurement by a clear, unambiguous margin in every orientation — used only when the dimensional incompatibility is mathematically clear.