Today a 3/4 mattress is not considered a standard size
A 3/4 mattress is not considered a standard size but rather a custom size these days. The size of a ¾ bed is usually 48 inches wide to 74.5-75 inches long. This size is best for a single sleeper. There are mattress owners that have discovered that their 3/4 mattresses can be up to two inches wider or shorter than the usual measurement.
If you have a bed frame that requires a 3/4 mattress they may need to be specially ordered as many stores do not stock them but they can be ordered. If you have the original mattress and are looking for a new mattress it is best to measure that mattress in case you are one of the 20% whose mattress is not 48”x75”. In this case your mattress may need to be custom made so you need to be careful on your measurements.
A 3/4 mattress size is in between a twin and a full size mattress. The twin and full mattresses are standard sizes therefore easier to find.
Twin mattress 39” wide x 75” long
Twin xl 39” wide x 80” long
3/4 mattress 48” wide x 75” long
Full 54” wide x 75” long