How To Tell Size Of Mattress: Simple Ways To Check Your Bed Dimensions
If you’re wondering how to tell size of mattress—especially when buying new sheets, a bed frame, or replacing your mattress—you’re not alone. Mattress sizes can be confusing, and small differences in measurements matter more than many people expect.
This FAQ-style guide walks you through how to measure your mattress, how to match your measurements to standard sizes, and what to watch for when your numbers don’t fit neatly into a chart.
How do I measure my mattress to find its size?
To figure out how to tell size of mattress, start with a tape measure and a flat surface.
Strip the bed
Remove all bedding, toppers, and pads. Measure the mattress only.Measure the width
Measure from left edge to right edge at the widest point.
Note the number in inches (or centimeters, if you prefer).Measure the length
Measure from head to foot, along the longest side.Measure the height (thickness)
Measure from bottom to top surface. This doesn’t affect the size name (twin, queen, etc.), but it does help with choosing fitted sheets and bed frames.
Write the numbers down as Width × Length × Height. For size identification, the first two are most important.
What are the standard mattress sizes?
Once you have your measurements, compare them to common mattress dimensions. Sizes can vary slightly by manufacturer, but most follow these general measurements:
| Mattress Size | Approx. Width × Length (inches) |
|---|---|
| Twin | 38" × 75" |
| Twin XL | 38" × 80" |
| Full (Double) | 54" × 75" |
| Queen | 60" × 80" |
| King | 76" × 80" |
| Cal King | 72" × 84" |
If your numbers are within about 1–2 inches of one of these, that is usually the size you have.
My measurements don’t match exactly—what does that mean?
When working out how to tell size of mattress, it’s normal to see slight differences between your measurements and a size chart.
Common reasons include:
- Rounding differences: Some mattresses are listed in whole inches even if they’re slightly off in real life.
- Edge style: Rounded corners or pillow-top edges can make measurements tricky.
- Age and wear: Older mattresses may sag or compress slightly.
- Manufacturer variation: Different makers may be off by about an inch or so.
If the width and length are close to a standard size, use the closest match. For example:
- A mattress measuring about 59" × 79" is still typically considered a queen.
- One around 75" × 79" usually aligns with a king.
How can I tell the difference between two similar sizes?
Some sizes are easy to mix up. Here’s how to tell them apart:
Twin vs. Twin XL
- Twin: About 38" × 75"
- Twin XL: About 38" × 80"
If the length is around 80 inches, it’s likely a Twin XL.
Full vs. Queen
- Full: About 54" wide
- Queen: About 60" wide
If you measure around 60" wide, it’s probably a Queen, even if the length is similar.
King vs. California King
- King: About 76" × 80" (wider, slightly shorter)
- Cal King: About 72" × 84" (narrower, longer)
If your mattress is wider than it is long by only a small amount, it’s likely a King. If it’s noticeably longer but a bit narrower, that points to California King.
Does mattress thickness affect the size name?
No. Thickness does not change the size category. A 10-inch and a 14-inch mattress can both be queens if the width and length match queen dimensions.
However, thickness matters for:
- How your sheets fit
- The look of your bed on the frame
- How high the sleeping surface feels
When buying bedding, check that the pocket depth of fitted sheets matches your mattress height.
What if my mattress seems non-standard?
If, after measuring, your mattress is several inches off from any size:
- It may be an older or regional size.
- It might be a custom-made mattress.
- It could be designed for a specific type of bed (such as RVs or small spaces).
In that case, you may need “oversized,” “deep pocket,” or custom” bedding and should rely on your exact measurements rather than a size name.
✔️ Quick Mattress Takeaways
Key points about how to tell size of mattress:
- Always measure width and length with bedding removed: write them down clearly.
- Compare to standard sizes and choose the closest match within about 1–2 inches.
- Twin vs. Twin XL: look for 75" vs. 80" length.
- Full vs. Queen: width is the giveaway—around 54" vs. 60".
- King vs. Cal King: king is wider, Cal king is longer and a bit narrower.
- Thickness doesn’t change the size name, but it does impact sheet fit.
- If your measurements don’t match any standard size closely, treat your mattress as non-standard and shop by exact dimensions, not just the label.
Understanding how to tell size of mattress makes it much easier to choose fitting sheets, protectors, and frames, and helps you avoid the frustration of bedding that just doesn’t quite fit.
