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What Size Crib Mattress Do I Need?

Find the right crib mattress size from your crib type and safety-fit requirements with practical guidance for standard and mini crib setups.

Direct answer

For a full-size crib, use a crib mattress that is at least 27.25" x 51.25" and no more than 6" thick. For mini or non-full-size cribs, match the crib maker dimensions exactly instead of guessing from a standard mattress label.

crib type first, then mattress dimensions, thickness, and snug fit
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Crib mattress fit guide

Mattress type
Full-size crib mattress
Crib type: 1 full, 2 mini
type
Crib inside width
in
Crib inside length
in
Mattress thickness
in
Mattress size
At least 27.25" x 51.25"
Thickness
6" or thinner
Fit check
Interior crib dimensions are in the full-size range

Use the crib label and manufacturer instructions as the final authority, especially for mini and non-full-size cribs.

Crib mattress sizing by crib type

Full-size crib

At least 27.25" x 51.25"

Thickness must not exceed 6"

Mini crib

Use crib-specific dimensions

Mini crib sizes vary by model

Portable or non-full-size crib

Match the maker label exactly

Do not substitute a standard mattress

Unknown crib

Stop and identify the crib

Do not buy by appearance alone

Why this page is stricter than a decor guide

Crib mattress sizing is a safety fit question, not a styling question. The page gives a quick shopping answer, but the crib label and manufacturer instructions should always be treated as the final source.

Safe fit workflow

  1. 1Identify whether the crib is full-size, mini, portable, or another non-full-size type.
  2. 2Read the crib label and manual for the required mattress dimensions.
  3. 3Check mattress thickness against the crib instructions.
  4. 4Do not use a mattress that leaves an unsafe side gap or does not match the crib class.

FAQ

What is the standard crib mattress size?

For a full-size crib, the mattress must be at least 27.25" x 51.25" and no more than 6" thick. Always confirm the crib label and instructions before buying.

Are all crib mattresses the same size?

No. Full-size crib mattresses follow a regulated size range, but mini cribs and other non-full-size cribs need the exact mattress dimensions specified by the crib maker.

How snug should a crib mattress fit?

It should fit snugly against the crib sides with no unsafe gap. If the crib is mini, portable, or otherwise non-full-size, do not guess from a standard mattress label.

Sources & method

We reviewed these references while writing this answer. Figures are estimates — confirm safety-critical work with a professional. Last updated June 7, 2026.