Instagram post images by API: sizes, carousels and publishing

An Instagram feed post made from a template is a quote card, an announcement, a testimonial, a carousel slide or a photo collage with your brand's layout and this week's words. With Shareglint you render it from data — one request per post, a batch for the month — as a JPEG, because that is the only format Instagram's publishing API takes. This page covers the sizes, carousels and automatic publishing; the cross-network workflow is on social media images.

The two sets of numbers

Instagram has two sets of rules, and they differ.

In the app — when someone uploads by hand — a photo keeps its resolution when it is 320 to 1080 pixels wide with an aspect ratio between 1.91:1 and 3:4, that is "a width of 1080 pixels with a height between 566 and 1440 pixels". Other ratios are cropped, smaller photos enlarged to 320 px wide, larger ones scaled down to 1080 px (Instagram Help).

Through the Content Publishing API — when a tool posts for you — an image must be JPEG, at most 8 MB, with an aspect ratio "within a 4:5 to 1.91:1 range", between 320 and 1440 pixels wide (scaled up or down to fit) and in sRGB (Meta for Developers, IG User Media, read 2026-11-06). The tallest ratio the API accepts is 4:5, not the 3:4 the app allows.

So for anything that may be posted automatically, stay between 4:5 and 1.91:1. The presets that fit both sets of rules:

Files come out at twice the preset size by default (portrait is 2160×2700); the API scales anything wider than 1440 px down, and a manual upload is scaled to 1080 px. Add "scale": 1 if you want the file at exactly 1080 px wide.

One post

curl -X POST "https://shareglint.com/v1/images?wait=true" \
  -H "Authorization: Bearer sk_live_..." \
  -H "Content-Type: application/json" \
  -d '{
    "template": "testimonial-stars",
    "size": "portrait",
    "format": "jpeg",
    "modifications": {
      "quote": "We cut our weekly reporting from a day to an hour.",
      "rating": "5",
      "name": "Ana Ruiz",
      "role": "Head of Ops",
      "company": "Northwind"
    }
  }'

format: jpeg is the important line: a PNG is fine for a manual upload, but Instagram's API rejects it — "JPEG is the only image format supported" (Instagram content publishing). JPEG quality is 85 by default; set quality up to 100 for type-heavy designs. The same values again return the same file for free.

Carousels

A carousel is a cover, slides and a closing slide. Render them from the carousel templates, all in the same size: Instagram crops every carousel item "based on the first image in the carousel", 1:1 by default, and allows up to 20 items per carousel (Instagram content publishing documentation, above).

# Cover and end slide: one request each. Slides: one batch.
curl -X POST "https://shareglint.com/v1/batches" \
  -H "Authorization: Bearer sk_live_..." \
  -H "Content-Type: application/json" \
  -d '{
    "template": "carousel-slide",
    "sizes": ["square"],
    "format": "jpeg",
    "rows": [
      { "id": "2", "index": "2", "total": "6", "heading": "Measure one thing", "body": "Pick the number your team can move this month." },
      { "id": "3", "index": "3", "total": "6", "heading": "Write it down", "body": "A goal in a chat thread is a wish." }
    ]
  }'

GET /v1/batches/{id} returns each slide's URL with its id, so you can list them in carousel order. Rows per batch by plan: Free 50, Starter 500, Pro 1,000, Scale 2,000, Business 5,000.

Publishing automatically

Shareglint makes the image; posting it is Instagram's API (or your scheduling tool, which uses that API). The flow Meta documents:

1. The account must be an Instagram professional account — business or creator (Instagram Platform overview).
2. POST /<IG_ID>/media with image_url set to the rendered JPEG's URL creates a container. Meta fetches the file itself, so it "must be on a public server" — the URL from the render is.
3. POST /<IG_ID>/media_publish with creation_id set to the container's id publishes it.
4. For a carousel, create a container per item with is_carousel_item=true, then one CAROUSEL container listing their ids, then publish that.

Limits to plan around: containers expire after 24 hours, and the number of API-published posts per day is capped — the content publishing page says 100 posts in a 24-hour moving period in one place and 50 in its carousel notes (read 2026-11-06), so check GET /<IG_ID>/content_publishing_limit rather than relying on either.

No-code tools work the same way: in n8n or Make an HTTP step renders the JPEG and a second step posts its URL through Meta's API.

Design notes

• Text size. The feed shows a post at a fraction of its pixel size; keep headlines short and large. Long text shrinks to fit its box in the built-in templates.
• Brand. accent and theme on every template keep a month of posts consistent.

Cost

One render per image; a six-slide carousel is six renders, the same slides again are free. The Free plan's 100 renders a month carry a watermark. Starter is $9 a month for 2,000 renders (pricing).

What it does not do

• It does not post to Instagram or store your Instagram token; your code or scheduler does that with Meta's API.
• It does not write captions or hashtags.
• It does not apply Instagram filters, music or stickers — those exist only inside the app.
• It cannot post to personal accounts: Instagram's API is for professional accounts only.