---
title: "Kids Mattress Guide (Cot to Single)"
description: "Plain UK guide to children's mattress sizes from cot to Single, with bunk depth and safety notes."
url: "https://bedguide.co.uk/sizing/kids-mattress-guide/"
category: "sizing"
primary_entity: "kids mattress guide"
date_published: 2026-08-03
date_modified: 2026-08-03
---

# Kids Mattress Guide (Cot to Single)

> Children's mattresses go from cot bed (~70 × 140 cm) to Small Single (75 × 190 cm) and Single (90 × 190 cm). Cot mattresses must fit the cot snugly for safety. Kids' beds and bunks often limit mattress depth for guardrails. Support growing bodies without adult marketing extremes — follow cot and bunk depth and safety rules first.

## Dimensions

| Size name | Width (cm) | Length (cm) | Width (in) | Length (in) |
| --- | --- | --- | --- | --- |
| Cot bed (Verify against specific cot) | 70 | 140 | — | — |
| Small Single | 75 | 190 | — | — |
| Single | 90 | 190 | — | — |

## Size ladder

Children usually move through stages. Exact centimetres beat age myths.

| Stage | Typical size idea | First check |
| --- | --- | --- |
| Cot / cot bed | Model-specific (often ~60×120 or ~70×140 cm bands) | Snug fit — no gaps |
| Small Single | 75 × 190 cm | Room and bed type |
| UK Single | 90 × 190 cm | Standard next step for many older children |

Details: [cot and Small Single](/sizing/cot-and-small-single-sizes) and the full [kids size journey](/sizing/kids-bed-size-journey).

## Safety rules that outrank marketing

1. **Infant safer-sleep guidance** comes from health authorities — not mattress ads  
2. **Cot fit** must be snug to the manufacturer’s size  
3. **Bunk / high sleeper** age, weight and guardrail rules are mandatory reading — [bunks](/beds/bunk-beds-and-high-sleepers)  
4. **Mattress depth** on bunks protects rail height  

Compare layouts: [bunk vs high sleeper](/compare/bunk-vs-high-sleeper).

## Firmness without adult slogans

Growing bodies need a supportive, even surface. Extreme “hotel soft” pillow-tops are rarely the first kids need. Adult [soft/medium/firm](/mattresses/spring-tension-vs-comfort-feel) labels still mix support and quilt — teach the difference early.

## Common mistakes

- Buying a deep adult mattress for a bunk that only allows a thin one  
- Assuming every “cot bed” mattress is interchangeable  
- Skipping the [assembly](/beds/assemble-a-bunk-bed) and rail checks

## Related BedGuide entries

- [UK sizes](/sizing/uk-standard-bed-sizes)
- [Learning path: Kids sleep sizes](/learn/kids-sleep-sizes)
- [How to choose a mattress](/mattresses/how-to-choose-a-mattress)

## Frequently asked questions

### When should a child move to a Single mattress?

When height, climbing behaviour and carer judgement say the cot or Small Single is outgrown. There is no single age. Safety and rail rules on bunks still apply.

### Can adults use a kids mattress?

Size may fit a Single frame, but construction and weight limits may be lighter. Check stated limits on the label.

### How thick can a bunk mattress be?

Only as thick as the bunk maker allows so guardrails stay high enough. Measure the rail and read the frame instructions before buying a deep adult-style mattress.

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Source: https://bedguide.co.uk/sizing/kids-mattress-guide/ · BedGuide — educational encyclopedia, no affiliate commission. Facts checked against official sources where possible; see https://bedguide.co.uk/editorial-policy. Report an error: https://bedguide.co.uk/corrections.