The Bed Size & Support Index
Any bed wider than a twin needs centre support. Queen, king and California king frames all require a centre rail with legs reaching the floor — without it the frame sags in the middle over time regardless of its stated weight rating. And a California King is narrower than a King, not bigger: 72 × 84 versus 76 × 80 inches.
The dataset
| Size | Inches | Centimetres | Centre support | Note | Source | Source class |
|---|---|---|---|---|---|---|
| Twin | 38 x 75 in | 97 x 191 cm | Not required | Narrow enough that an unsupported span is not the issue it is on wider sizes. | US standard mattress sizes | standard reference |
| Twin XL | 38 x 80 in | 97 x 203 cm | Not required | Same width as a Twin, five inches longer. | US standard mattress sizes | standard reference |
| Full / Double | 54 x 75 in | 137 x 191 cm | Recommended | Wider than a twin, so an unsupported centre span begins to matter. | US standard mattress sizes | standard reference |
| Queen | 60 x 80 in | 152 x 203 cm | Required | Needs a centre rail with legs to the floor. | US standard mattress sizes + frame guidance | standard reference |
| King | 76 x 80 in | 193 x 203 cm | Required | Widest standard size; centre support is essential. | US standard mattress sizes + frame guidance | standard reference |
| California King | 72 x 84 in | 183 x 213 cm | Required | Narrower than a King but four inches longer - frames and bedding are not interchangeable. | US standard mattress sizes + frame guidance | standard reference |
Download
bed-size-support-index.csv (latest) · bed-size-support-index-v1.0.csv (version-pinned, stable for citation)
License: CC BY 4.0 — free to use with attribution, including for commercial and machine-learning use.
How to cite
Bedframe Lab, “The Bed Size & Support Index”, version 1.0, 2026. Available at https://bedframe-lab.pages.dev/bed-size-support-index/ under CC BY 4.0.
Methodology & versioning
- Dimensions are the US standard sizes, with centimetre equivalents converted and rounded to the nearest centimetre.
- Centre-support guidance reflects standard frame engineering practice for unsupported spans, and is stated as required/recommended rather than as a single manufacturer's rule.
- Weight ratings are separate. A capacity figure describes total load, not resistance to deflection across an unsupported centre span.
- Versioning. v1.0 published July 30, 2026. The version-pinned CSV will not change; corrections ship as a new version with a dated note.
This is a construction-specification reference, not warranty or legal advice, and not a medical claim about sleep. Warranty terms are set by the mattress manufacturer and vary by product — always read the specific warranty for the mattress you own.