Foundations · Twin XL
Twin XL box spring dimensions
Current Twin XL foundations measure about 38–39 × 79.5–80 inches (96.5–99.1 × 202–203.2 cm). Some manufacturers call this Twin Long.
Semrush US · 4,400 searches/mo · KD 19| Label or calculation | Dimensions | What it means |
|---|---|---|
| TEMPUR Twin Long | 38 × 80 in (96.5 × 203.2 cm) | Same nominal top as Twin XL. |
| Beautyrest Twin XL | 39 × 79.5 in (99.1 × 201.9 cm) | One inch wider in this finished example. |
| Sealy Twin Long | 38 × 79 in (96.5 × 200.7 cm) | One inch shorter than the nominal mattress length. |
Twin XL and standard Twin foundations are different lengths; do not infer fit from width alone.
Twin XL length matches Queen and King
The nominal 80-inch length is why two Twin XL units form a Split King footprint. Finished foundation examples may be slightly shorter to fit the frame.
Check adjustable-base compatibility separately
A rigid foundation and an adjustable base are different products. Use only the support type approved for the mattress and frame.
Measurement method
Start with the product and space you actually have.
- 1
Measure the frame opening. Record inside width, length, support ledges, and center support.
- 2
Check finished dimensions. Use the foundation specification, not only the size label.
- 3
Add vertical layers. Combine frame support height, foundation, mattress, pad, and topper.
- 4
Verify the support system. Follow the mattress and frame manufacturers’ current requirements.
Questions, answered
Frequently asked questions
Can a Twin mattress use a Twin XL box spring?
The foundation is roughly five inches longer, so the footprint does not match. Use the intended mattress and frame dimensions.
Are two Twin XL foundations a King foundation?
Many King foundation sets use two similarly sized pieces, but finished widths vary. Buy or verify the matched King configuration.