1. Measure the platform, not just the old mattress
Remove bedding and measure the inside of the sleeping platform from side to side, then head to foot. An old foam mattress can compress or change shape, so use its measurements as a cross-check rather than your only reference. Take measurements at more than one point if the walls or frame taper. Record width × length in inches.
2. Check the height you can actually use
Measure clearance beneath shelves, windows, cabinets, and a closed slide-out. For a bunk, follow the bed manufacturer’s maximum mattress thickness and guardrail requirements. If the bed lifts for storage, check both its clearance and the lift system’s weight limit. A taller mattress can also change how fitted sheets and covers fit.
3. Look for corners and moving parts
A rounded corner, cutout, or hinged platform can turn a rectangular size into a custom order. Photograph the platform, draw a simple diagram, and label every dimension. Send the diagram to the manufacturer for written confirmation before ordering. Check drawer and door travel with the planned mattress height in mind.
4. Match the numbers, then the name
Three-quarter usually points shoppers toward 48 × 75 inches, but short full can mean 48 × 74. Short queen can be 60 × 74 or 60 × 75. Our finder keeps those sizes separate. A nearby size is a comparison to investigate, not a fit guarantee.
5. Confirm the order details
Confirm the exact variant, finished dimensions, manufacturing tolerance, thickness, weight, foundation requirements, and return terms. Special dimensions or cutouts may change return eligibility. Save the order configuration and the seller’s written confirmation.
Research notes
Size examples and product distinctions are based on the manufacturers’ published specifications. For an exact product, use its model guide and linked sources.
