How to measure your bed for a custom-size mattress
3 min read · Updated 25 September 2026
A step-by-step way to measure an odd-sized bed, built-in bed or cot so a made-to-measure mattress fits the first time.
What you need
A metal measuring tape, a pencil and five minutes. Remove the old mattress first.
Step by step
1. Measure the length of the base inside the frame, from headboard to footboard, at the left edge, the middle and the right edge. Write down the smallest.
2. Measure the width at the head, the middle and the foot. Again, use the smallest.
3. Check the corners. Built-in beds are not always square. If the diagonals differ by more than half an inch, tell us when you order.
4. Measure the lip depth if the bed has a raised edge, so you can choose a thickness that sits right.
Leave a little room
For a bed with a frame on all sides, take about a quarter of an inch off each measurement so the mattress slides in and the sheets fit. For an open platform, use the exact size.
Order it
Enter your length and width in the custom size tool to see the exact price, worked out per square foot. Custom sizes take 5–7 extra days to make and cannot be returned, so measure twice.
Still deciding?
Four questions, one recommendation, with the reasons.