Ghost ships with a content delivery network that automatically resizes images. Upload a 4000×3000 PNG, and Ghost serves readers a 720px WebP instead—unless your theme requests a different size, or the image format doesn’t support transformation, or you hit one of several quiet edge cases.
Most operators assume the CDN “just works.” It mostly does. But understanding what triggers a transform, what gets served as-is, and how Ghost bills for bandwidth saves you from surprise overage invoices and layout shifts when images don’t resize as expected.
What formats transform and what gets passed through
Ghost’s CDN—hosted on Cloudflare for Ghost(Pro) plans and configurable for self-hosted installs—applies transformations to JPEG, PNG, and WebP uploads. It converts them to WebP or AVIF (depending on browser support) and resizes them based on the srcset attributes your theme declares.
GIF files do not transform. Neither do SVGs. Upload a 2MB GIF, and every reader downloads the full 2MB, regardless of viewport size. Same with SVG: no resize, no format conversion. Ghost serves them byte-for-byte as uploaded.
This matters if you’re embedding animated illustrations or icon libraries. A single large GIF in a popular post can chew through your monthly bandwidth allocation in hours. Check your Ghost analytics bandwidth report (Settings → Labs → Beta features → Enable staff users) to see per-post transfer totals. If one post accounts for 40% of your monthly bandwidth, check for un-transformed assets.
Resize breakpoints and theme control
Ghost doesn’t decide image sizes on its own. Your theme’s {{img_url}} helper or <img srcset> markup tells the CDN which widths to generate. The default Casper theme requests 300w, 600w, 1000w, and 2000w variants. If your theme doesn’t declare a srcset, Ghost serves the original upload—no resize.
Custom themes sometimes hardcode a single image URL without size parameters. When that happens, readers on mobile download the same 2000px file as desktop users. You’ll see this in your bandwidth logs: high transfer volumes from mobile user agents.
The fix: audit your theme’s image partials. Look for <img src="{{img_url}}"> without a size argument or srcset. Replace with <img srcset="{{img_url size='s'}} 300w, {{img_url size='m'}} 600w, {{img_url size='l'}} 1000w, {{img_url size='xl'}} 2000w" sizes="(max-width: 800px) 400px, 800px">. Ghost’s CDN generates those variants on-demand and caches them.
What you pay and when costs spike
Ghost(Pro) plans include bandwidth: 50 GB on the Starter plan ($11/month), 350 GB on Creator ($31/month), and 1 TB on Team ($63/month). Overages cost $1 per GB on Starter, $0.50 per GB on Creator, and negotiated rates on Team.
Image transforms themselves don’t cost extra—they’re included in the CDN—but cache misses drive up bandwidth. Each new transform (a new size or format combination) counts as a fresh origin request and CDN delivery. If your theme declares ten srcset widths and your CDN cache TTL is short, you’re generating and serving ten variants per image per cache expiration cycle.
Ghost’s CDN cache is tied to Cloudflare’s edge network. Time-to-live defaults to one year for transformed images, but purging your CDN cache (via Ghost admin or API) invalidates all variants. If you purge after every post publish, you’re forcing full re-transforms for your entire image library every time. That’s fine for a 20-post blog. It’s expensive for a 2,000-post archive.
One operator I talked to in August saw bandwidth jump from 80 GB to 240 GB in a single month after switching themes. The new theme requested five additional srcset widths. Ghost generated five new variants for every image in every post ever published, then served all of them to returning readers whose browsers requested the new sizes. Cost: $80 in overage fees on a Creator plan.
One non-obvious tip: preload hero images with explicit dimensions
Ghost’s image CDN is reactive. It doesn’t pre-generate transforms until a reader requests a specific size. If your post’s hero image is above the fold and your theme doesn’t preload it, readers see layout shift while the browser waits for the CDN to resize and deliver the image.
Fix it by adding explicit width and height attributes to hero images in your theme’s post template. Ghost’s CDN still transforms the image, but the browser reserves layout space immediately. Add <link rel="preload" as="image" href="{{img_url feature_image size='xl'}}"> in your post head partial for above-fold images. The CDN delivers the transform faster, and Core Web Vitals improve.
Most operators never touch Ghost’s CDN settings. But if you’re seeing unexpected bandwidth bills, slow image loads, or layout shifts on mobile, start by checking which formats you’re uploading, what your theme requests, and whether your cache purge strategy is forcing expensive re-transforms.
Got a Ghost CDN question or a bandwidth story? Reply to this email—I read every one, and operator experiences often become future articles.