Crib Mattress Size and Dimensions

This crib mattress size calculator checks a mattress width, length and optional thickness against the US federal limits quoted on this page, and reports whether each number is within or outside them. It runs in your browser, is free, and needs no sign-up. Nothing you enter is stored or uploaded. A table lists every limit with its source, drawn from 16 CFR 1241.2 and the CPSC page on full-size baby cribs.

Use it when you have a crib mattress in hand, are checking a replacement, or want to see how the published numbers fit together. It makes no safety claims. Results are calculated from your inputs and the limits quoted from the named sources.

How to use the Crib Mattress Size Calculator

1. Choose “Crib type”: full-size crib, or mini or other non-full-size crib.
2. Choose “Measure in”: inches or centimeters. Your entries use the unit you choose.
3. Enter the “Mattress width”, the short side.
4. Enter the “Mattress length”, the long side.
5. Optionally enter the “Mattress thickness (optional)”. For a mini crib this field is hidden. To skip the thickness check on a full-size crib, leave it empty.
6. Read “Against the limits quoted” first. It states whether the mattress is within the limits quoted and names any dimension that is outside them.
7. Check the “Width”, “Length” and “Thickness” lines for each dimension separately.
8. If the length falls between 51 1/4 in and 51 5/8 in, read the warning. It means the two published minimums differ.
9. Read the “Corner gap rule” line. It states the 3.15 in (80 mm) corner gap limit from the mattress test. The calculator does not measure a gap for you.
10. Below the results, the table “Your mattress against the limits” marks each dimension Within or Outside, and “Limits quoted from the federal rules” lists every number with its source.

The presets fill the form with example values: “At the minimum” (27.25 × 51.625 × 6 in), “27.5 × 51.75 × 5 in”, “70 × 132 × 12 cm” and “Mini crib”. Use them to see how the outputs change before entering your own measurements. The Mini crib preset shows only the “Mini cribs” line with the rule for after-market mattresses, because the calculator does not check sizes for mini cribs.

What are the US federal minimums for a full-size crib mattress?

For a full-size crib, 16 CFR 1241.2(b)(1)(i) sets the minimum mattress size at 27 1/4 in (690 mm) wide and 51 5/8 in (1310 mm) long. A mattress smaller than either figure falls outside the limits quoted on this page.

The same paragraph sets a corner gap limit of 3.15 in (80 mm) in the mattress test. That paragraph states no thickness limit. The CPSC page “Full-Size Baby Cribs” says a full-size crib mattress must be no thicker than 6 in, and it gives the length as 51 1/4 in instead of 51 5/8 in. The calculator shows both published figures and checks against the longer one. A length between 51 1/4 in and 51 5/8 in triggers a warning.

CPSC business guidance on 16 CFR part 1219 gives the full-size crib interior as 28 ± 5/8 in wide by 52 3/8 ± 5/8 in long (71 ± 1.6 cm by 133 ± 1.6 cm). The interior is the space inside the crib, not the mattress, so these numbers answer a different question.

How does the calculator check a crib mattress size, including mini cribs?

The calculator converts every entry to inches, using the exact rule 1 in = 2.54 cm. It then compares each dimension with its limit: width must be at least 27.25 in, length at least 51.625 in, and thickness no more than 6 in. For example, 70 cm is 27.56 in, which passes the width minimum, while 69 cm is 27.17 in, which fails it.

Worked example 1: a mattress of 27.5 × 51.75 in and 5 in thick has a width at or above 27.25 in, a length at or above 51.625 in and a thickness within 6 in. The overall line is within the limits quoted.

Worked example 2: a mattress of 27 × 51.5 in and 7 in thick has a width below 27.25 in and a length below 51.625 in, though above the CPSC page’s 51.25 in. Its thickness is above 6 in. The overall line is outside the limits quoted for all three dimensions.

The calculator also shows warnings for values outside sanity bounds: width outside 10 to 60 in, length outside 20 to 90 in, thickness over 12 in, or width larger than length. These bounds are not federal limits. A warning usually means a measurement needs checking.

For a mini crib, 16 CFR 1220.1 defines the type by interior size: length over 55 in (139.7 cm) or under 49 3/4 in (126.3 cm), or width over 30 5/8 in (77.7 cm) or under 25 3/8 in (64.3 cm). That rule sets no mattress dimensions. Under 16 CFR 1241.2(b)(2), an after-market mattress for a non-full-size crib must be at least the same size as the original mattress or larger.

Sources (checked 15 October 2026): law.cornell.edu · cpsc.gov · law.cornell.edu · cpsc.gov

Worked examples

Calculated by the tool above; open it with the same values to see each step.

Frequently asked questions

What is the minimum crib mattress size for a full-size crib?

Under 16 CFR 1241.2(b)(1)(i), a full-size crib mattress must measure at least 27 1/4 in (690 mm) wide and 51 5/8 in (1310 mm) long. The calculator flags any mattress smaller than either figure.

Why does the calculator show two different lengths?

The CPSC page “Full-Size Baby Cribs” gives the minimum length as 51 1/4 in, while the regulation text gives 51 5/8 in. The calculator shows both and checks against the longer figure. If your length is between the two, it warns you that the published minimums differ.

Does the calculator check mattress thickness?

Yes, against the 6 in maximum given on the CPSC page. The regulation paragraph quoted here sets no thickness limit. The thickness field is optional, so leave it empty to skip the check.

What does “within the limits quoted” mean?

It means the measurement falls inside the numbers quoted on this page. It is not a certification or a safety finding, and the page makes no safety claims.

Can I enter measurements in centimeters?

Yes. Set “Measure in” to centimeters, and the calculator converts your entries to inches using 1 in = 2.54 cm exactly. For example, 70 × 132 cm equals 27.56 × 51.97 in.

What if my crib is a mini crib?

The calculator does not check mattress sizes for mini cribs, and the thickness field is hidden. Under 16 CFR 1241.2(b)(2), an after-market mattress must be at least as large as the original mattress.

Related tools

• Mattress Size Chart and Bed Dimensions: use it to compare other mattress sizes and bed dimensions with the crib figures here.
• Bed Sheet Sizes: Fitted, Flat and Pocket Depth: use it to check sheet dimensions and pocket depth for a mattress.
• Baby Blanket Sizes: use it to find common baby blanket dimensions when you are shopping for a crib.
• Comforter Size Chart: use it to compare comforter sizes for the other beds in the house.
• Standard Pillow Size Chart: use it to match pillow sizes to your beds.
• Blanket Size Chart: use it to compare blanket sizes across bed types.