Vehicles & Transport calculator
What Roof Box Size Fits My Car?
Use usable roof length between hatch/windscreen limits, roof-bar spread, roof box length to find roof-box car fit.
Enter your measurements
What Roof Box Size Fits My Car uses usable roof length between hatch/windscreen limits, roof-bar spread, roof box length and the other configured measurements to return roof-box car fit with a formula written specifically for this tool.
- Usable roof length between hatch/windscreen limits — Required
- Roof-bar spread — Required
- Roof box length — Required
- Box minimum bar spread — Required
- Box maximum bar spread — Required
- Rear hatch clearance requirement — Required
Roof-box car fit
Enter the measurements above to calculate roof-box car fit.
How the calculation works
V9 calculation: lengthPass=boxLength≤max(0,roofUsableLength-hatchClearance); spreadPass=boxMountMinSpread≤roofBarSpread≤boxMountMaxSpread; overallPass=lengthPass AND spreadPass. The result is reported as roof-box car fit.
Worked example
Example: Usable roof length between hatch/windscreen limits = 100 cm; Roof-bar spread = 50 cm; Roof box length = 70 cm; Box minimum bar spread = 50 cm; Box maximum bar spread = 50 cm; Rear hatch clearance requirement = 30 cm. Result: Fits; Spread Pass = Pass; Length Pass = Pass.
Before you decide
Use the finished, usable dimensions after trim, handles, skirting, packaging or other projections where relevant. This page calculates the stated geometry or quantity only; product-specific construction or installation details can still affect the final choice. For what roof box size fits my car, the limiting result on this page is roof box vehicle fit.
Direct measurement/geometry calculation. No external reference is required for the arithmetic itself; the result is derived only from the user-entered measurements and the formula stored in calculationLogicJson.
Frequently asked questions
What does the Roof Box Size Fits My Car calculator tell me?
It returns roof box vehicle fit from the measurements entered on this page. The calculation is specific to roof box size fits my car, so the result should be compared with the exact product or specification you are considering.
Which measurements should I take for roof box size fits my car?
Measure usable roof length between hatch/windscreen limits, roof-bar spread, roof box length, box minimum bar spread, box maximum bar spread, rear hatch clearance requirement. Use clear, usable dimensions rather than nominal room or product labels.
Should I round the roof box vehicle fit?
Keep the calculated value for comparison, then choose a real product that meets or stays within the returned roof box vehicle fit while allowing for the clearances, tolerances or ratings shown by its manufacturer.