#Why the crosshair will not hold a ratio
If you have ever needed a stack of screenshots that all sit at the same proportions, for a slide deck, an App Store listing, a thumbnail set, or a docs page, you have run into this. You press Command + Shift + 4, drag, and macOS gives you a live pixel readout beside the crosshair but no way to say "keep this 16:9 while I drag". Photoshop has fixed-ratio marquees. Snipping tools on other platforms have them. The macOS capture UI does not.
Search for a Mac screenshot aspect ratio setting and you land on the same answer everywhere: there is not one in the capture UI. So people drag, squint at the readout, undershoot, retake, and eventually accept something that is 1601 by 902 and call it close enough. That works until the images sit next to each other and the mismatch shows as a wobble in the layout.
The good news is that the ratio problem is really a rectangle problem, and macOS has always had an exact way to specify a rectangle. It just is not in the crosshair.
#The exact way: screencapture -R
Every Mac ships with a screencapture command, and its -R flag takes a rectangle as x, y, width, height. Choose a width and height in your target ratio and the capture cannot come out wrong:
# 16:9, starting at the top-left corner of the screen screencapture -R 0,0,1600,900 shot.png # 4:3, offset 100 points in from the corner screencapture -R 100,100,800,600 shot.png # -x silences the shutter sound screencapture -x -R 0,0,1600,900 shot.png
I ran each of these on a MacBook running macOS 26.3 with a 3024 by 1964 Retina display, then read the results back with sips. The measured output:
| Ratio wanted | Rectangle passed | File produced | Ratio delivered |
|---|---|---|---|
| 16:9 | -R 0,0,1600,900 | 3200 × 1800 | exactly 16:9 |
| 4:3 | -R 100,100,800,600 | 1600 × 1200 | exactly 4:3 |
| 16:9 odd size | -R 0,0,1000,563 | 2000 × 1126 | 16:9 to the pixel |
Measured on macOS 26.3 on 21 July 2026. Your pixel numbers will differ on a non-Retina or scaled display; the ratios will not.
Two things fall out of that table. The rectangle is given in points, and the file arrives in backing pixels, which on this Retina display means everything doubles. That surprises people who asked for 1600 wide and got a 3200-wide PNG. It is not a bug and it does not touch the ratio: 3200 by 1800 is the same 16:9 as 1600 by 900. If you need the smaller file, scale it down afterwards rather than capturing a smaller region, because capturing smaller throws away detail you cannot get back.
The other thing: -R needs coordinates, which means knowing where on screen the thing you want lives. For a window in a predictable spot that is fine. For arbitrary content it is easier to capture generously and crop, which is the next section.
#Capture loose, crop to ratio
The other built-in tool is sips, the image utility that has shipped with macOS for years. Its -c flag crops to a height and width, in that order, from the centre of the image:
# crop a capture down to exactly 1600 x 900 sips -c 900 1600 shot.png # check what you actually got sips -g pixelWidth -g pixelHeight shot.png
Running that on the 1600 by 1200 capture from the table returned exactly 1600 by 900, cropped from the middle. Note the argument order, height before width, which trips up everyone including me the first three times.
One warning worth stating plainly: sips rewrites the file in place. There is no undo. Copy the original first, or point it at a duplicate, unless you are certain. That is the entire workflow for a batch: take screenshots however you like, duplicate the folder, then crop every file to the ratio in one loop.
If what you are after is a whole scrolling page rather than a rectangle of screen, that is a different problem with different tools, and I covered it separately in the guide on full-page screenshots on the Mac.
#Doing it by eye when you must
Sometimes you are mid-conversation and not about to open Terminal. Two things make the freehand path less painful.
First, watch the readout. The crosshair reports the size of your selection as you drag, so you can steer toward numbers you recognise. Pick round targets you can hit: 1600 by 900, 1280 by 720, 800 by 600. Hitting a round number by eye is easier than hitting an arbitrary one, and any 16:9 pair works as well as any other.
Second, use Command + Shift + 5 rather than Command + Shift + 4 when you need several captures of the same region. It gives you a selection rectangle that stays put between captures, so once you have dragged one good frame you can capture repeatedly at that exact size without redoing the drag. It is not a ratio lock, but for a sequence of shots it is the closest thing macOS offers.
Both paths are approximate on the first drag and exact after it. That asymmetry is why I reach for the command when the shots need to match.
#Where all those screenshots end up
Bias declared: I build NotchBay, so treat this as the maker describing his own app. The part of screenshotting that nobody plans for is the aftermath. Ratio-hunting means retakes, retakes mean five near-identical PNGs, and by the end of the afternoon your desktop is a wall of Screenshot 2026-07-21 at 14.22.11 files.
Two habits help. Copy to the clipboard instead of the desktop when the shot is disposable, by adding Control to the usual shortcut, which puts the image on the clipboard and never writes a file. And keep a clipboard history so the ones you copied are still reachable ten minutes later. NotchBay holds roughly the last sixty clips in a tray inside the notch, images included, and runs text recognition over them so a screenshot of a URL is findable by typing part of that URL. Details are in the clipboard tray write-up, and the general copy-paste mechanics in how to copy on a Mac.
None of that fixes the ratio problem. It fixes the mess the ratio problem leaves behind, which in my experience is the part that actually costs the afternoon.
#Frequently asked questions
Can macOS lock a screenshot to a fixed aspect ratio?
Not in the crosshair selection. There is no modifier that constrains the drag to 16:9 or 4:3. The reliable ways are to pass an exact rectangle to the screencapture command in Terminal, or to capture loosely and crop to the ratio afterwards. Dragging by eye against the live pixel readout gets you close but rarely exact.
Why is my screenshot twice the size I selected?
Because Retina displays store two image pixels per point. On my MacBook running macOS 26.3, capturing a 1600 by 900 rectangle produced a 3200 by 1800 PNG. The aspect ratio is unaffected: both are exactly 16:9. If you need the smaller number, scale the file down afterwards rather than selecting a smaller area.
How do I crop an existing screenshot to 16:9?
Use the built-in sips command with the crop flag and your target height and width, for example sips -c 900 1600 shot.png. It crops from the centre of the image. On my Mac a 1600 by 1200 capture became exactly 1600 by 900. Work on a copy, because sips rewrites the file in place.
Does the screencapture command need permission?
Yes. Whatever app you run it from, usually Terminal, needs Screen Recording permission under Privacy and Security in System Settings. Without it the command still runs but the resulting image will not contain your screen contents. Grant it once and the app keeps the permission.
