The State of Web Vitals

Iframe dimensions set

Whether iframes declare dimensions - unsized iframes shift layout.

Field data PhoneDesktopAll Scope All sites Q1 2026 edition · All devices field outcomes
Metric LCP INP CLS
1

At a glance the headline numbers for Iframe dimensions set

Whether iframes declare dimensions - unsized iframes shift layout.

2
Categories
In the distribution
68.4%
Fleet share
Top: has_none
35.4%
Sites with any
Of has_none

68.4% of iframes declare no dimensions.

The State of Web Vitals · Q1 2026 · 94,910 sites · all devices field datacorewebvitals.io/state-of-cwv
2

The iframe dimensions set mix who uses what, and how fast each group loads

Median LCP (sites using feature)
0
0.5s
1s
1.5s
2s
2.5s
3s
3.5s
4s
Has none1.6s68% of sites
Has dimensions1.7s32% of sites
VariantShare of sitesMedian
Has none
68%
1.6s
Has dimensions
32%
1.7s

Iframe dimensions set. On the fleet: 68.4% has none, 31.6% has dimensions. 35.4% of sites use at least one has_none.

Lowest-share bucket: LCP 1.4s. Highest-share bucket: LCP 1.6s. r = +0.25.

The State of Web Vitals · Q1 2026 · 94,910 sites · all devices field datacorewebvitals.io/state-of-cwv
3

Passing LCP per bucket every category and count level at once - color is the pass rate

1
2
3
4
5
6
7
8
9
Has none 68.4%
84
80
81
80
81
80
81
79
78
Has dimensions 31.6%
84
79
77
78
76
72
72
← few of this category on the pagemany →
60%95%+ of sites passing LCP Faded cells: under 100 sites

Each row is a category, each column its own count bucket (few on the left, many on the right); the cell is the share of those sites passing LCP.

Has dimensions swings the hardest: 84% of sites pass LCP with few, 72% with many. computed

The State of Web Vitals · Q1 2026 · 94,910 sites · all devices field datacorewebvitals.io/state-of-cwv
4

Few vs many - does quantity cost LCP? the pass rate with few vs many of each category

60%70%80%90%100% few → many
Has dimensions 31.6% 84% → 72%
Has none 68.4% 84% → 78%
% of sites passing LCP · hollow ring = pages with few, solid dot = pages with many

Per category: the pass rate among pages with FEW of it (hollow ring) against pages with MANY (solid dot), worst trend first. Thin buckets are excluded from the endpoints.

More Has dimensions costs the most: the LCP pass rate falls from 84% with few to 72% with many. computed

The State of Web Vitals · Q1 2026 · 94,910 sites · all devices field datacorewebvitals.io/state-of-cwv
5

Why this matters for the Core Web Vitals, and where to start fixing it

An iframe without dimensions is a box of unknown size. The browser guesses, the embed loads, the box resizes, and everything below it jumps. That is the CLS pattern for embeds: maps, videos, forms, ads.

Reserve the slot. Width and height (or aspect-ratio on the container) make the size known before the content arrives, and the late embed lands without moving anything.

How does this affect the Core Web Vitals?

Of the 2 categories, Has none separates passing sites from failing sites the most. Where Has none is rare: 90% pass the CLS. Where it is common: 85%.

Go fix it Perfect YouTube Core Web Vitals → Google Maps with 100 percent PageSpeed → CLS from images and media →
Related signals Scripts per page → DOM depth → DOM size → Page weight & requests → Chrome field data from 94,910 sites, representing millions of real page loads · How we measured