Hello I bought a foam mattress (king size) on the amazon prime day for a really good price, also purchased metal box springs just to help support it and keep the mattress off the floor. My wife and I put everything together a noticed the mattress overhangs the box springs by .5 of an inch all around. My main question is, is this normal? I’ve never had a foam mattress before so I don’t know if this is common or not.
Here is a photo:
Hi dtweaponx,
Welcome to the Mattress Forum! 
The ISPA (International Sleep Products Association) standard sizing for mattresses are as follows:
Size Dimensions
Twin 38 x 74½
Twin Extra Long 38 x 79½
Full 53 x 74½
Full Extra Long 53 x 79½
Queen 60 x 79½
Eastern King 76 x 79½
California King 72 x 83½
Even though these are the “standard” sizes for ISPA … there can still be some variation between the “standard” sizing made by different manufacturers in the industry. With soft goods like mattresses there can also be variations between different mattresses as well (normally in the range of a +/- 1" variation from their standard sizing) depending on the dimensions of the materials when they are cut (there can be some variance with cutting flexible materials) and the components they use in their mattresses and on the thickness of the cover that encloses them (a cover that is 1/2" thicker or thinner for example would change the length and width of the mattress by 1").
There could also be a variation in the dimensions of your foundations, and together this could add to the discrepancy.
I hope that helps explain things.
Phoenix
Hi Phoenix,
Our new eastern King size mattress was just delivered. We ordered it from one of the Trusted Members here. Their website states that a king is “76x80”. Our mattress is 74.5" x 78" which is a 1.5" x 1.5"-2" variation. Sooooo…we’re not sure if we want to quibble about this. However, our new platform bed will be delivered tomorrow and we’ll see if there is a noticeable gap. I would appreciate your feedback as to whether this size difference is a reasonable thing to ask them to correct? There is a 100 day trial regardless. We love the mattress and really don’t want to start shopping around for another.
Every mattress manufacturer will have different allowable variances when it comes to dimensions of mattresses. The law tag on your mattress should have the dimensions of the mattress on it.
Even if it says 74.5", like Phoenix says, there can be a 1 to 1+1/2 inch variable. The “standard” dimension we use on the east coast for a king size mattress is 76" x 80". On all of the law tags that I’ve ever seen they all read 75.5" x 79.5".
The dimensions of the Foam that your manufacturer uses can also contribute to dimensional variances as well.
We sell futon mattresses as well as regular bed mattresses, and the futons are always smaller than regular mattresses, so they can look even smaller on a real bed frame!
The problem comes when the dimension of your actual mattress, if it is 74.5", is 1+1/2 inches smaller than that dimension.
It can be a no-win situation when you bring this up to the store or manufacturer.
[quote=“Paul S.” post=79909]
The problem comes when the dimension of your actual mattress, if it is 74.5", is 1+1/2 inches smaller than that dimension.
It can be a no-win situation when you bring this up to the store or manufacturer.[/quote]
Hi Paul,
Thanks for your reply.
I understand the variation. The mattress is a traditional pocketed coil innerspring with a latex comfort layer on top. There is no memory foam. There is steel coil, not foam, around the perimeter for edge support. If I had purchased their wood frame foundation, I suspect that would have measured 76 x80 due to the materials. And then the foundation would stick out. My prior mattress, an innerspring and box spring were the exact same size and measured 76 x 79.5. I purchased the mattress directly from the manufacturer. I will contact them and see what they say.
