Measure the inside of the cot where the mattress sits, and check the manual’s permitted thickness before ordering. The outside dimensions of the frame and the name “standard cot” do not confirm mattress size.

What you need

• A tape measure with centimetre markings.
• The cot or playpen’s brand, model name and manual.
• A clear photo of the mattress support area and any size label.

Step 1: Find the manufacturer’s requirements

Look for the specified mattress dimensions, maximum thickness and any requirement to use the original mattress. Keep the original instructions with your measurements. For playpens and travel cots, do not order an additional mattress unless the manufacturer explicitly permits it.

Step 2: Measure the usable internal length and width

With the cot empty and assembled according to its instructions, measure the internal length along the mattress support area. Then measure the internal width. Repeat at several points to check whether the opening is even. Record all measurements in centimetres; do not round up to the next advertised mattress size.

Measure the space itself, not an old compressed mattress or the outside of the cot. If corners are curved, photograph them and include that detail in your enquiry.

Step 3: Record the maximum mattress thickness

The height of the mattress affects how much cot side remains above the sleep surface. Follow the cot’s stated thickness limit and any mattress-height marking. Do not choose a thicker mattress just to fill a space.

Step 4: Compare the listed product dimensions

For example, a cot manual that permits only a thinner mattress does not become compatible with a 10 cm mattress simply because its length and width match. Check every requirement before ordering.

Step 5: Send a complete enquiry if anything is unclear

Copy this checklist into your custom-size request:

• Cot or playpen brand and model.
• Manual’s specified mattress dimensions and thickness limit.
• Measured internal length and width at more than one point.
• Photos of the empty support area, corners and size label.
• Your delivery postcode and preferred mattress model.

Wait for our confirmation of available construction, final dimensions, price and production lead time. Do not pay a custom deposit until the specification has been agreed. If the equipment requires its original mattress, follow that requirement.

When your mattress arrives

Check the delivered item against the order and the equipment manual before use. If the fit, thickness or condition is wrong, contact us before using it. Do not fill gaps with towels, pillows or extra padding.

Compare our mattress models · Read the buying guide · Check care instructions