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The bedroom dimensions matter more than the berth count when you already own mattresses. Start with the inner floor plan for the exact tent version, then compare the widest and longest points of every bed you intend to use.
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Use inner measurements
The external tent length can include porches, living space and the gap between the inner and flysheet. It cannot establish mattress fit. Look for a separate inner diagram and check whether a quoted width refers to one bedroom or several combined.
Dividers can change the usable arrangement. Find out which panels are removable and whether there are fixed seams, doors or support points that prevent a mattress sitting where your sketch suggests.
Add the actual mat widths
Three 51cm mats need 153cm of width; three 64cm mats need 192cm. Neither calculation includes spare clearance. A three-person label therefore cannot tell you that three wide mats will fit.
The current MSR Elixir 3 specification lists a 213 × 178cm floor. In that example, three 64cm mats exceed the published width by 14cm. Older Elixir generations have different dimensions, so use the plan belonging to the tent being sold.
Match the bed variant too
Regular, wide and long versions can share similar product names. For an example of a defined standard width, compare the regular Therm-a-Rest NeoAir XLite NXT on Amazon UK with the manufacturer’s size options. Confirm the selected size rather than using a measurement from another variation.
Measure an existing airbed fully inflated in normal use. Include any projecting valve or frame where it affects the layout. Do not plan to squeeze a bed against the walls to compensate for an undersized room.
Look above floor level
Sloping walls narrow the space around a thicker mat or raised camp bed. Check clearance at the head and foot with the sleeping bag occupied. The inner should not be forced into contact with the flysheet by bedding or luggage.
For camp beds, check the frame and feet as well as the sleeping surface. Protect the groundsheet using a suitable method that does not create an unstable support.
Keep the room usable
Draw the door opening and leave space to get in and out. Include the overnight items that must remain indoors and decide where bags will go. A layout that fills the entire rectangle may be mathematically possible but awkward every night.
Use a tape outline on the floor at home for a first check, then try the pitched tent where possible. Buy the combination of bed and bedroom that gives everyone a practical sleeping position and an accessible exit.
Continue with our camping tent guide.
Reviewed 10 September 2026. This guide is based on published specifications and guidance.