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.