WordPress 画像サイズ早見表
WordPress の画像サイズに関する決定版リファレンス。登録されているすべてのサイズと実際の寸法、どれが強制トリミング（ハードクロップ）されるか、2560px の -scaled しきい値、WooCommerce のサイズ、そして用途ごとに何をアップロードすべきかを解説します。
See it on your own image — open the Image Size LabCore sizes
Registered on every stock WordPress install.
| Name | Size | Crop | Editable in admin? |
|---|---|---|---|
| thumbnail | 150 × 150 | hard crop | Settings → Media |
| medium | 300 × 300 | fit | Settings → Media |
| medium_large | 768w | fit | No UI |
| large | 1024 × 1024 | fit | Settings → Media |
| 1536x1536 | 1536 × 1536 | fit | No UI |
| 2048x2048 | 2048 × 2048 | fit | No UI |
medium_large (768w) and the two retina sizes have no admin UI at all — you would not know they exist from the dashboard. And any upload over 2560px on its longest edge also gets a -scaled copy, which WordPress then serves in place of your original.
WooCommerce sizes
Added when WooCommerce is active. Configure under Appearance → Customize → WooCommerce → Product Images. Defaults have shifted between Woo versions, so treat these as indicative and check your own install.
| woocommerce_thumbnail | 300 × 300 | hard crop |
| woocommerce_single | 600w | |
| woocommerce_gallery_thumbnail | 100 × 100 | hard crop |
What to actually upload
Guidance by purpose — not registered sizes, just sensible source dimensions.
Covers the social-share ratio and downscales cleanly for in-theme use. The single safest default.
Wide enough for large screens, under the 2560px -scaled threshold so your original is served as-is.
Matches the medium_large / large range most themes actually display.
Ship it larger than you show it; WordPress downscales cleanly, it never upscales.
WordPress requires a minimum of 512 × 512 and crops it square.
The 1.91:1 ratio Facebook, LinkedIn and X expect. WordPress will not generate this; your SEO plugin picks the closest size.
Common mistakes, and the real cause
Image looks blurry after upload
Cause: Your image was over 2560px on its longest edge, so WordPress made a "-scaled" copy and is serving that instead of your original.
Fix: Disable or raise the big_image_size_threshold, or upload under 2560px.
Thumbnail cuts off heads
Cause: thumbnail hard-crops to a 150 × 150 square by default, centre-cropped — anything off-centre gets cut.
Fix: Upload with the subject centred, or register a custom size with a different crop.
Uploads folder is enormous
Cause: WordPress stores one file per registered size. Core makes 6 plus the original; a theme and WooCommerce add more.
Fix: Stop generating sizes you do not use with intermediate_image_sizes_advanced.
large / 1536 / 2048 version is missing
Cause: WordPress never upscales. If your upload is smaller than a size, that size is simply not generated.
Fix: Upload a larger source image.
Responsive images (srcset) look low quality
Cause: A size that srcset depends on — usually medium_large (768w) — was removed.
Fix: Keep medium_large; it exists mainly to feed srcset.