A standard twin bed mattress generally measures 39 inches wide and 74 to 75 inches long, depending on the manufacturer. Extra-long twin mattresses measure 80 inches long. Toddler beds, when converted from a crib, use the same mattress from the crib with dimensions of 27 inches wide and lengths in 51 1/2 to 52 inches.
A junior mattress varies in size by the manufacturer and can be 60 inches long, but nowadays they are mostly standard twin-bed size. Junior twin mattresses used to range in size from the toddler bed or crib-sized mattress up to 31 inches wide and 75 inches long. Older junior mattresses used to be about 66 inches long, suitable for a child just over 4 feet tall.
When it's time to move a child from a crib to a bed, especially if he's climbing out of the crib, the crib mattress can make the move to a toddler bed. These mattresses work the best for that in-between stage when a child is ready for more independence but may need the protection a crib mattress affords during the potty-training stage. Parents generally move their child from a crib to a toddler bed between the ages of 1 1/2 to 3 1/2.
The Move to a Twin Bed
Whether you choose between a junior twin mattress or a standard twin, the best age to move your child to the larger bed is after the child no longer wets at night. Children 4 years of age to about 6 or 7 fit comfortably on a junior twin mattress when the mattress is about 66 inches long, as the average 4-year-old is 37 inches tall, while the average 7-year-old is 44-inches tall.
For older children with enuresis -- a nighttime bed wetting problem -- leaving them on a crib-sized toddler mattress may do more psychological harm than good. To protect a junior or standard twin mattress for children with enuresis, purchase a waterproof, hypoallergenic cover.
What Mattress to Buy
To avoid the added expense of having to buy three mattresses for your growing child, a more cost-efficient solution would be to use the crib mattress in a toddler bed until the child grows enough to require the standard or extra-long twin mattress. Because crib and toddler mattresses are interchangeable, a crib mattress may work for a child up until the age of 5 or 6. After that age, a standard twin can work as a bed all the way through the child's teen years, unless your child's growth rate exceeds the norm; then it might be wiser to choose an extra-long twin mattress instead.
Mattress Size Based on Height
Children grow at different rates, but your child's height should be a major factor when changing the mattress and bed. According to a chart offered by the state of New Mexico, the average height sizes across the United States for children range as follows:
- 2 years old, 31 inches
- 3 years old, 33 inches
- 4 years old, 37 inches
- 5 years old, 40 inches
- 6 years old, 42 inches
- 7 years old, 44 inches
- 8 years old, 45 inches
- 9 years old, 49 inches
- 10 years old, 51 inches
- 11 years old, 52 inches
- 12 to 13 years, 58 to 62 inches
- 14 to 15 years, 63 to 66 inches
Because all children are different and grow at their own pace, don't get caught up in marketing and advertising recommendations as to when to move your child to a larger bed. When your child is ready for a standard or extra-long twin, your child will let you know that she is too grown-up for that cutesy toddler race car, train or princess bed.
As a native Californian, artist, journalist and published author, Laurie Brenner began writing professionally in 1975. She has written for newspapers, magazines, online publications and sites. Brenner graduated from San Diego's Coleman College.