What Size Is My Mattress? How to Measure and Match It to Standard Bed Sizes

If you’re asking “What Size Is My Mattress?”, you’re likely trying to buy new sheets, a bed frame, or replace your current mattress and want to be sure of the right size. This guide walks you through how to measure your mattress, how those measurements compare to common mattress sizes and dimensions, and what to do if your mattress doesn’t quite match standard sizing.

How do I figure out what size my mattress is?

To answer “What size is my mattress?”, start by measuring it. You only need a tape measure and a few minutes.

Step-by-step:

1. Strip the bed
   Remove all bedding, toppers, and pads so you’re measuring the actual mattress.

2. Measure the length
   Measure from the head of the mattress to the foot, in inches or centimeters.

3. Measure the width
   Measure from side to side, at the widest point.

4. Measure the height (thickness)
   Measure from the bottom to the top surface. Thickness doesn’t change the “size name,” but it matters for deep-pocket sheets and fitted covers.

Write down your measurements. Your mattress “size” is determined by length and width, not height.

How do my measurements compare to standard mattress sizes?

Once you’ve measured, compare your numbers to common mattress sizes. Small variations of about an inch are normal due to materials and manufacturing.

Here is a simple reference table using typical U.S. dimensions (L x W):

If your measurements are very close to one of these, that is likely your mattress size.

Why does knowing my mattress size matter?

Knowing the answer to “What size is my mattress?” helps with several everyday decisions:

• Buying bedding: Fitted sheets, protectors, and comforters are cut to specific sizes.
• Choosing a bed frame or base: Frames are built to match standard dimensions.
• Planning your bedroom layout: Length and width affect how much floor space you have.
• Sharing the bed: Couples often find larger sizes more comfortable.

A mismatch between your mattress size and your bedding or frame can cause slipping sheets, poor fit, and discomfort.

What if my mattress doesn’t match any standard size exactly?

It’s common for mattresses to be off by an inch or so, especially after years of use or with certain materials. Consider:

• Small differences (about 1")
  Usually still fit the closest standard size bedding and frames.

• Larger differences (2" or more)
  Your mattress could be:

  • An older sizing standard
  • A non-standard or custom size
  • Designed for a specific type of frame

In these cases, you may need flexible or oversized bedding, or items labeled as “fits multiple sizes” rather than tightly tailored options.

How can I tell if I have Twin, Twin XL, Full, Queen, King, or California King?

Here are some simple clues based on your measurements and how the bed feels:

Twin vs. Twin XL

• Twin: Around 75" long, suitable for most children and shorter adults.
• Twin XL: Around 80" long, same width but extra legroom.

If your mattress is about 38" wide and closer to 80" long, it’s likely a Twin XL.

Full vs. Queen

• Full (Double): About 75" x 54", wider than Twin but shorter than Queen.
• Queen: About 80" x 60", longer and wider, often preferred for couples.

If your mattress is about 60" wide and 80" long, it’s most likely a Queen.

King vs. California King

• King: About 76" wide and 80" long, wider than it is long.
• California King: About 72" wide and 84" long, narrower but longer.

If you have a very long mattress but it seems a bit narrower, you may have a California King.

Does mattress thickness change its size name?

No. The height or thickness (for example, 8", 12", or 15") does not change the official size of your mattress. A Queen mattress is a Queen whether it is thin or very thick.

However, thickness does matter for:

• Fitted sheets (you may need “deep pocket” or “extra deep pocket”)
• Mattress protectors and encasements
• Edge height when getting in and out of bed

What if my bed frame and mattress size don’t match?

If you’re wondering “What size is my mattress?” because something feels off with your bed frame, here are signs of a mismatch:

• Noticeable gaps between mattress and frame or headboard
• Mattress overhangs the frame
• Sheets fit the mattress but not well within the frame

When this happens, rely on your measured mattress dimensions, then select frames, bases, and bedding that match that size, even if the current frame is different.

✅ Quick Mattress Takeaways

Key points to understand about “What Size Is My Mattress”

• Measure first: Length and width determine size; height is separate.
• Compare to standards: Match your numbers to common sizes (Twin, Full, Queen, King, etc.).
• Expect minor variation: Up to about 1" difference is common and usually not a problem.
• Thickness doesn’t rename the size: It only affects how your sheets and bedding fit.
• Look for clues in proportions: Narrow and long often means Twin XL or California King; wide and shorter may mean Full or standard King.
• Trust your measurements over assumptions: Mattress labels and frame sizes can be misleading or outdated.

By carefully measuring and comparing to standard dimensions, you can confidently answer “What size is my mattress?” and choose bedding and bedroom furniture that fit comfortably and correctly.