**********************MAKING FITTED SHEETS FROM FLAT SHEETS***********************
After searching the internet, I’ve come up with the following as “standards” (loosely speaking) for bedding sizes. I’ve also discovered that some of the extra deep newer mattresses (some with pillow tops) are 16 to 20 inches deep and would take a great deal more fabric to start with and make a difference in the size of the corner cut-outs.
Since beds come in different sizes, so do the sheets covering them. Sheet sizes are determined by the length and width of the bed and come in the following categories: twin, double, queen, king and California king. These sheet sizes are seen throughout the industry.
Sheet sizes are fairly standard except for the "pocket" measurement on fitted sheets. This tells the shopper/sewer how "deep" the sheet is, in case he or she has an extra thick mattress, or one with a pillow-top. So, if you have a thick mattress, look for a deeper pocket, ensuring the sheet will be a good fit.
As a rule, sheet sizes are (for fitted sheets):
TWIN - 39 inches (99 centimeters) wide by 75 inches (191 centimeters)
DOUBLE - 54 inches (137 centimeters) wide by 75 inches (191 centimeters)
QUEEN - 60 inches (150 centimeters) by 80 inches (201 centimeters)
KING - 80 inches by 80 inches (203 centimeters)
CALIF KING72 inches (183 centimeters) by 84 inches (213 centimeters)
A shopper can expect sheet sizes to be 20 to 30 inches (51 to 76 centimeters) longer and wider for the fitted sheets in each size.
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STANDARD MATTRESS SIZES + mattress depth added for drop on all four sides
CRIB: 26 x 48 IF the sides are 5” deep, then add 10 in. to each dimension for total of approx 36 x 58
Add tuck under of 4 inches each side = approx 44 x 66
TWIN: 39 x 75 IF the sides are 8” deep, then add 16 in. to each dimension for approx 55 x 91
Add tuck under of whatever amount you have, at least 3+ inches if possible, or go to next larger sheet
Example, a standard twin TOP sheet is 66 x 96, maybe enough to make a twin FITTED sheet
DOUBLE: 54 x 75 IF depth = 10” then add 20 in. to each dimension for total of approx 74 x 95
Add tuck under of whatever amount you have, at least 3+ inches if possible, or go to next larger sheet
Example: standard DOUBLE flat sheet is 81 x 96, this is too close to make the fitted bottom. If it were me, I’d use this for a twin, or go to a queen size to make my double fitted bottom sheet.
QUEEN: 60 x 80 IF matt depth = 11” add 22 in. to each dimension or approx 82 x 102
Add tuck under of whatever amount you have, at least 3+ inches if possible, or go to next larger sheet
Example: standard queen FLAT is 90 x 102, that’s not big enough – go to a king size, or use your queen flat for a full or twin bed.
KING: 80 x 80 IF matt depth = 12” then add 24 in. to each dimension for approx 104 x 104
Add tuck under of whatever amount you have, at least 3+ inches if possible, or go to next larger sheet, but it's not likely you'll find a larger sheet, instead you would need to piece on the ends and sides.
To make a King fitted sheet from a King flat you should measure VERY carefully to see if you have enough. Remember you have to have some “tuck under” and you might possibly need to add material on the bottom and sides to make the fitted sheet big enough, especially if you have a very deep mattress.
CAL KING: 72 x 84 IF matt depth = 12” then add 24 in. to each dimension for approx 96 x 108
Add tuck under of whatever amount you have, at least 3+ inches if possible, or go to next larger sheet, but it's not likely you will find a sheet any larger. Instead you would have to add to the sides and the ends but be sure to put any seams on the edges of the sheet, not on the part where you sleep - it would be very uncomfortable there.
Same as above.