Measure three directions
With the stroller folded as instructed, measure its greatest length, width and height, including handles and wheels. Record whether the seat or wheels were removed. Leave useful clearance around the folded shape.
Inspect the route into storage
A rectangular box calculation can compare six orientations. It cannot model a sloping boot opening, wheel arches, a latch or the lifting motion. Test the real stroller in the real vehicle before relying on a fit.
Secure it as directed
Follow the vehicle and stroller instructions for storage and load security. Never infer load capacity from an empty-space calculation.