OBS Canvas Scaling Calculator
Compare the base canvas, scaled output, and a camera or screen source before you change OBS settings. The calculator shows scale percentages, aspect-ratio conflicts, empty bars, crop amounts, and pixel load in one practical plan.
Map the complete OBS sizing path
Choose common presets or type exact dimensions. Results update whenever a width, height, preset, or placement mode changes.
Your scaling blueprint
Configuration notes
- The canvas and output share one aspect ratio, so output scaling does not add bars.
- The 4K source is reduced evenly to fit the 1080p canvas.
What the OBS canvas scaling calculator measures
Source: pixels supplied
A camera, capture card, phone mirror, browser, image, or screen capture supplies a source resolution. This is the detail available before OBS positions the source. A sharp source can still be cropped or made hard to read when its placement is wrong.
Base canvas: the working board
The Base (Canvas) Resolution is the board on which sources are positioned. Fit, Fill, Stretch, and Native decide how a source occupies that board, revealing scale, unused canvas, or cropped overflow.
Scaled output: the delivered frame
The Output (Scaled) Resolution is the completed frame sent to an encoder or recording file. Comparing it with the canvas reveals whether the final resize is proportional and how many pixels each output frame contains.
The calculator first maps the source onto the base canvas using the selected placement mode.
It then compares the assembled canvas with the output, matching the order in which the composition is built.
How every result is calculated
horizontal scale = output width / canvas width
vertical scale = output height / canvas height
Equal percentages mean a proportional resize. Different percentages mean that the two frames use different aspect ratios and would be distorted if forced edge to edge.
fit scale = smaller of canvas width / source width and canvas height / source height
fill scale = larger of those two values
Fit protects the complete image and may leave unused space. Fill covers the canvas and may place part of the source outside it.
A worked 4K-to-720p example
A 3840 x 2160 camera fitted to a 1920 x 1080 base canvas uses a 50% scale on both axes. The complete 16:9 camera frame occupies the complete 16:9 canvas, so neither bars nor crop are added. Scaling that canvas to 1280 x 720 uses 66.67% on both axes. The output contains 921,600 pixels per frame instead of the canvas's 2,073,600 pixels, a reduction of about 55.56% in frame pixel count.
The camera is not being sent straight to 720p. It is first reduced for the base composition, mixed with every other source, and then the composed frame is reduced again for output. That distinction matters when text, overlays, or browser sources are created at small sizes. A tiny overlay does not regain detail merely because the camera began at 4K.
Fit, Fill, Stretch, or Native: which placement is suitable?
Fit
Use Fit when every edge matters: slide decks, game interfaces, screen tutorials, product views, or a camera shot with useful detail near the border. Any spare area can become a designed panel rather than accidental black space.
Fill
Use Fill when the frame must be fully covered and the source can lose some edge content. Centered talking-head cameras often tolerate a modest crop, but faces, captions, hands, or products near an edge still need a visual check.
Stretch
Use Stretch only when changing proportions is intentional. Stretch independently matches width and height, so circles may become ovals and people may look wider or narrower. The calculator reports both scale axes to make that distortion visible.
Native
Use Native to keep one source pixel equal to one canvas pixel. A smaller source leaves room around it. A larger source extends beyond the canvas unless it is moved or cropped. Native can protect crisp interface text at a planned size.
The best transform depends on the job of the source, not on a rule that every box must be full. If a portrait phone capture is fitted to a 16:9 canvas, large side areas are mathematically expected. Those areas can hold chat prompts, a topic card, a guest panel, or brand elements. Filling that same canvas with the portrait source would remove much of the top and bottom. The result area quantifies both choices before you commit.
How to interpret bars, crop, and uneven output scaling
| Result | What it means | Useful next check |
|---|---|---|
| Unused canvas width | The placed source is narrower than the base canvas, leaving space split between the left and right sides when centered. | Keep the designed side panels, change the canvas ratio, or choose Fill after checking what would be cropped. |
| Unused canvas height | The placed source is shorter than the canvas, leaving space above and below when centered. | Review whether a crop is acceptable, or use the spare band for captions and program information. |
| Horizontal crop | The rendered source extends beyond the left and right canvas edges. | Move the transform, reduce its scale, or protect edge content inside a camera-safe area. |
| Vertical crop | The rendered source extends beyond the top and bottom canvas edges. | Check headroom, lower-third graphics, subtitles, and any object held near the frame limits. |
| Unequal output axes | The canvas and output ratios differ, so a full-frame resize would change geometry. | Use matching ratios, or build the intended framing on a base canvas with the final output ratio. |
Aspect ratios are simplified in the display when they match a common form such as 16:9, 4:3, 1:1, or 9:16. Other dimensions appear as a decimal ratio. The exact width and height remain the controlling values. If you need to compare a less common frame, the resolution calculator offers another way to inspect ratio-equivalent sizes before setting OBS.
A practical OBS scaling workflow
Start with the delivery shape
Decide whether the program is intended for a wide, square, or portrait frame. Set the base canvas to that composition shape before arranging sources. Converting a completed wide composition into portrait output can squeeze every element or remove important side content.
Choose a canvas you can compose at
A 1920 x 1080 base canvas is a common wide workspace because source positions and graphic sizes are easy to reason about. A larger canvas offers more working pixels, but it also asks OBS to composite more pixels before output scaling.
Set output from delivery needs
Choose output dimensions with frame rate, bitrate, encoder capacity, and upload stability in mind. More pixels are not automatically clearer when the available bitrate is too low for motion. Test the complete chain rather than judging a paused local preview.
Transform each source deliberately
Fit screen captures when interface edges matter. Crop cameras only after checking body position and movement. Keep text sources large enough on the base canvas that the final downscale still leaves them readable on a phone.
Inspect at final output size
A large OBS preview can hide small labels and thin lines. View a recording or test transmission at the actual output dimensions. Check both a computer display and a phone-sized view when the audience commonly watches on mobile.
Save a known-good profile
Record the base, output, frame rate, transform mode, and any intentional crop. A copied calculator report gives collaborators a precise reference and makes it easier to restore the setup after an experiment.
Why a mathematically correct scale can still look soft
Inspect the source before scaling
Softness can begin before OBS scales anything. A camera may send a lower-resolution feed than its menu label suggests, a capture device may convert the signal, or a screen source may contain text rendered below its final display size. Confirm the source properties and inspect a still frame at full size. Enlarging a source creates more pixels, not more information.
Remove unnecessary resize stages
Repeated resizing can reduce edge clarity. A browser graphic might be rendered at 900 pixels wide, enlarged to 1100 pixels on the base canvas, then reduced with the complete canvas for output. Create text and line art close to their intended canvas size and avoid a small enlargement followed by another downscale.
Test motion, not only still frames
A 1080p frame that looks clean while still can break into blocks during a fast game or camera move if bitrate and encoder settings cannot preserve changing detail. Compare short recordings or test broadcasts with real movement, overlays, and audio. Use the calculator to settle sizing first, then evaluate encoding separately.
Keep encoder dimensions compatible
Odd widths or heights can be accepted in some paths but rejected or adjusted elsewhere. Even dimensions are safer for common video encoders, which is why the result notes flag odd values. A warning means you should verify what OBS and the selected encoder accept; it does not change the entered number.
OBS canvas scaling calculator FAQ
Should the base canvas and output resolution always match?
No. A larger base can be a convenient composition workspace while a smaller proportional output reduces transmitted pixels. Matching ratios avoids geometric distortion. Matching dimensions avoids the final resize, but it may require more encoding and upload capacity.
Is downscaling from 4K to 1080p always better than using a 1080p source?
No. The result depends on camera quality, capture path, lighting, focus, motion, and processing cost. A clean 4K source can provide useful detail when reduced, but the extra capture and scaling load may not improve a weak source or a small camera box.
Why does Fit add bars to a portrait source on a wide canvas?
Fit uses one proportional scale so the full portrait source remains visible. Its width reaches the limit before it can cover the wide canvas. The remaining side space is the geometric difference between the two aspect ratios.
Why can Fill crop more than I expected?
Fill uses the larger proportional scale so both canvas dimensions are covered. When ratios differ greatly, the other source dimension extends far beyond the canvas. The result reports total overflow on each axis; a centered placement splits that crop across opposite edges.
Does lower output pixel load mean lower computer use?
It can reduce some encoding work, but the base canvas, source decoding, filters, effects, frame rate, and encoder type also contribute. Pixel load is a useful comparison, not a complete computer-performance estimate.
Take the blueprint into a real framing check
Copy the report, apply the dimensions in OBS, and inspect a short recording before the broadcast. Then open BIGO LIVE and confirm that the delivery frame keeps faces, captions, screen detail, and calls to action inside a comfortable viewing area.
