Crib Mattress Fit Requirements: What Changed in 2026

Crib mattress fit requirements are the reason a compliant crib and a compliant mattress can still fail together. The crib passes its standard. The mattress passes its own standard. Put them in the same room and the space between them is what an inspector measures — and neither certificate covers it.

Two US rules moved in 2026. The crib mattress standard updated on 3 May 2026. The full-size crib standard updated on 1 August 2026. Both changes are about fit, not about materials. If your spec sheet still carries one interior dimension and one mattress size, it is now out of date in two places.

Crib mattress fit requirements are four numbers, not one

Crib mattress fit requirements are the dimensional limits that govern the crib's interior, the mattress's minimum size, and the space left between them — set by three separate documents across the US and EU, none of which is the "product dimension" a buyer normally asks you for.

Read that table twice and the trap is obvious. The crib is 28 in wide. The smallest legal mattress is 27 1/4 in wide. The standards do not meet in the middle.

Number 1: the interior is measured between the innermost surfaces

ASTM F1169 states the requirement precisely: the interior dimensions "shall be 28 ± 5/8 in. (71 ± 1.6 cm) wide as measured between the innermost surfaces of the crib sides and 52 3/8 ± 5/8 in. (133 ± 1.6 cm) long as measured between the innermost surfaces of the crib end panels, slats, rods, or spindles."

Three details in that sentence get lost in translation on the way to a catalogue page.

Innermost surfaces, not the frame. On a slatted crib the slats sit inboard of the rail. Measure to the rail and you will report an interior that is 15 to 25 mm larger than the one that gets tested.

At every mattress-support position. The standard requires both measurements "at the level of the mattress support in each of its adjustable positions." A crib whose sides taper — very common on cribs with a curved profile — can pass at the lowest setting and drift out at the highest.

Away from the corners. Measurements are taken no more than 2 in (5 cm) from the crib corner posts, or from the first spindle to the corresponding spindle at the other end. The corner is deliberately excluded from this check, because the corner has its own test. That is number 3.

If you publish a single interior figure with no datum, you have published a number nobody can verify. The reference values for the category are collected on the standard crib dimensions page; what your own drawing has to add is which surfaces the number runs between.

Number 2: the mattress minimum is smaller than the crib

The federal crib mattress rule sets a floor, not a match. As modified by CPSC, the requirement reads: "The dimensions of a full-size crib mattress shall measure at least 27 1/4 in. (690 mm) wide and 51 5/8 in. (1310 mm) long."

Do the subtraction. A nominal 28 in interior minus a 27 1/4 in mattress leaves 3/4 in across the width — call it 3/8 in per side if the mattress sits centred. Length behaves the same way: 52 3/8 in minus 51 5/8 in is another 3/4 in. Then add the tolerance. A crib at the top of its band (28 5/8 in) with a mattress at the minimum (27 1/4 in) is 1 3/8 in apart across the width, and every part of that is legal.

So the rules tolerate a gap on purpose. What they do not tolerate is the gap that opens up once a sheet goes on. That is where the real control sits.

Number 3: the corner gap is measured through a sheet washed twice

This is the number that actually governs fit, and it is the one most spec sheets have never heard of. From the same modified section: "When the mattress with the test mattress sheet is placed against the perimeter and in the corner of the crib, the corner gap shall not exceed 3.15 in. (80.0 mm)."

The mechanism matters more than the figure. CPSC's stated reason for adding this test was entrapment caused by "poor mattress fit from compression by sheets" — and the test sheet is deliberately shrunken by washing it twice before the measurement. A fitted sheet under tension pulls the mattress corners inward and rounds them. The bare mattress you measured on the factory floor is not the mattress that ends up in the crib.

Two practical consequences for a supplier:

• A mattress that passes at 27 1/4 in bare can fail once a shrunken sheet compresses its corners. Testing bare tells you nothing about compliance.
• The pass/fail is a system result. It depends on your mattress, the sheet, and the crib it is placed in. A mattress certificate on its own does not answer a buyer's question about a specific crib.

The single sentence worth quoting to a buyer: in the US the regulated number is not a side gap, it is a corner gap measured through a sheet that has been washed twice.

Number 4: in the EU the controlled number is a depth measured from a mark you print

EN 716-1:2017 approaches the same hazard from the opposite direction. Instead of measuring the gap, it fixes how deep the cot must remain once a mattress is in it.

The minimum distance between the upper side of the mattress base and the upper edge of the cot side and end must be at least 500 mm, measured under load per the test in EN 716-2:2017 §5.9.1. With the mattress base and sides in the high position, that vertical distance must be at least 200 mm, and the distance from the top of any foothold to the upper edge of the side must be at least 500 mm.

Here is the part that changes your labelling. Where the mattress is not an integral part of the cot, that measurement is not taken from the mattress base — it is taken from the mark of the maximum mattress thickness, and where the maximum thickness is given as text, the measurement takes that stated figure into account.

In other words, the EU makes you declare a maximum mattress thickness on the cot, and then measures your depth from the line you declared. Understate the thickness and your cot fails against your own mark. The 2017 revision also tightened marking under clause 7 and added a warning for cots with an integral mattress: "WARNING - this is a mattress, do not add a second mattress, suffocation hazards."

Two markets, two philosophies: the US controls a gap after a shrunken sheet; the EU controls a depth from a thickness you publish. A single "interior: 1300 × 700 mm" line satisfies neither.

What changed in 2026, and on which dates

The crib-side change is the one that quietly rewrites a dimension. ASTM notified CPSC of the F1169 revisions on 2 February 2026; the revised standard "adds new requirements for rigid barriers to address the risk of a child becoming entrapped between the mattress and a mesh sidewall." The new test method in section 7.26 states that with an outward horizontal force of 20 pounds applied to the barrier or barriers, "the interior dimensions of the crib shall be 28 in. ± 3/4 in. (71 cm ± 1.9 cm) width and 52 3/8 in. ± 3/4 in. (133 cm ± 1.9 cm) length."

Note what that does. The nominal interior is unchanged, but for a crib with a flexible sidewall the interior is now checked under load, and the tolerance widens from ± 5/8 in to ± 3/4 in because the wall is designed to move. The revision also adds "torn mesh/fabric" to the list of damaged components consumers are told to check, and a fall-hazard warning: "The product, including side rails, must be fully erected prior to use."

For context on how the mandatory baseline has moved: part 1219 originally incorporated ASTM F1169-10 with modifications, was updated to ASTM F1169-19 in 2019, and now runs on the 2025 edition. If your test report cites F1169-19, it cites the previous mandatory standard.

Why buyers keep asking, and what actually answers them

The pattern is always the same. Your listing says "interior 1300 × 700 mm." The buyer's compliance team writes back asking three things: between which surfaces, at which mattress-support position, and what maximum mattress thickness the cot is marked for. You answer in an email. Six weeks later a different person at the same buyer asks again.

The fix is not more numbers in a paragraph. It is a drawing where each dimension terminates on the surface it is actually measured from — interior width drawn between the innermost slat faces rather than the outer frame, the mattress-support positions called out as separate states, and the maximum mattress thickness drawn as a line on the side elevation exactly where EN 716-1 expects the mark to sit. That is a different job from photography, and a very different job from an AI-generated image: a generated picture will happily invent a plausible-looking dimension, while what compliance needs is the measured edge, snapped to the real geometry of the product and exported at the size the buyer's catalogue or the marketplace demands. Tolerance conventions for that kind of drawing are covered in product dimension tolerance, and the same nominal-versus-measured trap that catches lumber buyers is spelled out in nominal vs actual dimensions.

What to publish, item by item

• Interior width and length, each labelled with the surfaces the dimension runs between
• The mattress-support positions at which that interior dimension holds
• Minimum and maximum mattress size the crib is certified for, not just "fits standard mattress"
• Maximum mattress thickness, plus where the mark sits on the cot side, for EU shipments
• Whether sides are rigid, mesh or fabric, and whether rigid barriers are fitted
• The corner-gap result measured with a sheet fitted, stated as a number
• Standard edition and year on every claim: ASTM F1169-25, ASTM F2933-25, EN 716-1:2017

FAQ

What are the crib mattress fit requirements in the US?

Three numbers, held by two rules. The crib interior must be 28 in ± 5/8 in wide by 52 3/8 in ± 5/8 in long, measured between innermost surfaces, under the standard made mandatory by 16 CFR part 1219. A full-size mattress must be at least 27 1/4 in (690 mm) by 51 5/8 in (1310 mm) under 16 CFR part 1241. And with a test sheet fitted, the corner gap between mattress and crib must not exceed 3.15 in (80.0 mm).

How big a gap is allowed between a crib mattress and the crib?

The current federal rule does not set a single side-gap figure. What it limits is the corner gap with a shrunken test sheet installed: not more than 3.15 in (80.0 mm). EN 716-1:2017 in the EU works differently again, controlling the depth from the mattress base to the top of the cot side — at least 500 mm under load — measured from the cot's marked maximum mattress thickness.

What size mattress fits a full-size crib?

At least 27 1/4 in by 51 5/8 in (690 × 1310 mm), against a crib interior of 28 in by 52 3/8 in (71 × 133 cm). Both figures carry tolerances, so "it fits" is a test result rather than an arithmetic conclusion — which is why the corner-gap test exists.

Do I need a different spec diagram for the EU?

Yes, and it is a drawing difference rather than a translation. EU cots need the maximum mattress thickness shown as a mark on the side, plus the depth from the mattress base, while US buyers want the interior dimension tied to the innermost surfaces and a corner-gap result. The efficient answer is one annotated spec diagram per product carrying every datum both markets ask for, exported at each buyer's required image size — measured dimensions locked to the real edges of the product, so the same drawing survives a compliance review in either market.

When did the 2026 crib rules take effect?

The updated crib mattress standard, ASTM F2933-25, became mandatory on 3 May 2026. The updated full-size crib standard, ASTM F1169-25, became mandatory on 1 August 2026.

Sources & References

• Federal Register, 91 FR 6510 — Safety Standard for Crib Mattresses, direct final rule incorporating ASTM F2933-25
• Federal Register, 4 May 2026 — Safety Standard for Full-Size Baby Cribs, direct final rule incorporating ASTM F1169-25
• 16 CFR 1241.2 — Requirements for crib mattresses
• ASTM F1169 — Standard Consumer Safety Specification for Full-Size Baby Cribs, incorporated-by-reference text
• CATAS — Children's cots: news from the standardisation world, on the EN 716-1:2017 revision