DEVICE-FILL CROP LEDGER

TikTok Aspect Ratio

A 1080 × 1920 TikTok video does not automatically guarantee the same visible width on every phone. Under a fixed 1080 × 2400 cover-fill model, the video scales to 1350 × 2400, so the viewport cuts 135 displayed pixels from each side. In source coordinates, that is 108 pixels per side: only the center 864 of 1080 source pixels remains visible.

cover scale1.25×1920 → 2400 highdisplay crop135 px / sidein the 2400-high viewsource crop108 px / side80% width remains

A 1080 by 1920 TikTok source scaled to 1350 by 2400 behind a 1080 by 2400 viewport, with 135 displayed pixels cropped from each side — Displayed pixels and source pixels are different ledgers. At 1.25× scale, a 135-pixel screen-side cut corresponds to 108 pixels in the uploaded source.

Calculate the crop in both coordinate systems

Let the uploaded frame be S_w × S_h and the fixed viewport be V_w × V_h. A cover fit uses s = max(V_w ÷ S_w, V_h ÷ S_h). The displayed frame is S_ws × S_hs. For a centered fit, the displayed crop per side is (S_ws − V_w) ÷ 2.

To map the crop back to the upload, divide the viewport by the scale. The visible source width is V_w ÷ s, and the source crop per side is (S_w − V_w ÷ s) ÷ 2.

1080 × 1920 inside 1080 × 2400

s = max(1080/1080, 2400/1920) = 1.25
displayed frame = 1350 × 2400
display crop = (1350 − 1080) / 2 = 135 px per side

visible source width = 1080 / 1.25 = 864 px; source crop = (1080 − 864) / 2 = 108 px per side.

18:9 through 20:9: the same 9:16 upload, four different ledgers

These rows hold the viewport width at 1080 only to make the arithmetic comparable. The percentages are resolution-independent. If a portrait phone is described as T:9, the retained source-width fraction under centered cover is 16 ÷ T, and the crop fraction per side is (1 − 16/T) ÷ 2.

Fixed viewport	Cover scale	Displayed crop / side	Source crop / side	Source width retained
1080 × 2160 (18:9)	1.125×	67.5 px	60 px	960 px · 88.89%
1080 × 2280 (19:9)	1.1875×	101.25 px	85.26 px	909.47 px · 84.21%
1080 × 2340 (19.5:9)	1.21875×	118.125 px	96.92 px	886.15 px · 82.05%
1080 × 2400 (20:9)	1.25×	135 px	108 px	864 px · 80%

A 1080 × 1920 viewport has the same 9:16 ratio as the source, so this device-ratio crop is zero. A 20:9 cover viewport retains 16/20 = 80% of the source width and removes 10% from each source edge.

Device-fill crop is not the TikTok UI safe zone

A device-fill crop removes picture area at the viewport boundary. A UI safe zone reserves still-visible picture area so captions, buttons, usernames, or anchors do not cover it. One changes what is inside the viewport; the other changes what remains unobstructed. Do not subtract a generic safe-zone margin and call the result a crop.

TikTok's current Auction In-Feed Ads specification recommends 9:16 vertical creative at 540 × 960 or higher and says the safe zone varies with video dimensions, caption length, additional formats, and ad format. It also warns that preview and live appearance can differ because the preview is not device-specific. That is why this page gives a reproducible geometry model, not a universal TikTok margin.

Use the ledger without pretending every TikTok renders the same

1
Name the model
Use these figures only when a known viewport center-crops the video with a CSS-style cover fit.
2
Keep two ledgers
Record displayed crop for the viewport and source crop for editing. Never mix scaled screen pixels with upload pixels.
3
Separate critical content
Let backgrounds bleed to the edges, but keep faces, text, scores, and product details inside the narrower tested center.
4
Test the real post
Private-test on the actual devices and placements you care about. App mode, controls, captions, and device behavior can change the live result.

If the whole 9:16 composition must remain visible, place it over a full-bleed background rather than assuming a single edge margin fixes every device. The formula tells you what a chosen viewport would remove; it does not claim that TikTok always uses that viewport or fit mode.

TikTok aspect-ratio calculation questions

What is the best aspect ratio for a TikTok video?

9:16 is TikTok's recommended vertical orientation. A common full-HD canvas is 1080 × 1920, while TikTok's current Auction In-Feed Ads specification recommends at least 540 × 960 for vertical ads.

Why can a 1080 × 1920 video lose content on a taller phone?

If the player fills a viewport taller than 9:16 with a centered cover fit, it must scale the video until the height is filled; the enlarged width then extends beyond the viewport and is cropped at both sides.

How much of a 9:16 source is visible in a 20:9 cover viewport?

Its visible source width is 16/20 = 80%. For a 1080-pixel-wide upload, 864 source pixels remain and 108 pixels are removed from each side.

Is the calculated crop also a safe-zone recommendation?

No. It models aspect-ratio fill only. TikTok interface overlays are a separate obstruction, and their safe area varies by placement, caption, format, and device.

Calculation scope and sources

This page analyzes one explicit fixed-viewport cover model with square pixels and centered alignment. It does not assert that every TikTok surface uses cover, nor that every phone exposes its full physical screen as the video viewport. For a general missing-side calculation, use the image aspect ratio calculator; for exact 9:16 integer geometry, see the 9:16 aspect-ratio guide.

Platform claims were checked against TikTok's Auction In-Feed Ads specifications and vertical-video guidance. Every numeric crop above was independently recalculated from the stated source, viewport, and cover formula.