by 
Watch the tutorial
Step 1: Open the Sequence Settings
The aspect ratio belongs to your sequence, not to the clips inside it. To change it, make sure the sequence is active in the timeline, then go to Sequence > Sequence Settings in the top menu bar.
Step 2: Change the frame size values
In the Sequence Settings window, find Frame Size under Video. Two boxes show the horizontal and vertical size, and Premiere prints the resulting ratio right next to them.
For a vertical 9:16 video, type 1080 as the horizontal value and 1920 as the vertical value. The ratio label next to the boxes updates to 9:16 so you can confirm it. Other common choices follow the same idea: swap the numbers for a different shape such as a 1:1 square or a 16:9 widescreen frame.
Click OK. Premiere may warn that some preview files need to be deleted when you change the frame size. That is normal, so confirm and carry on.
Step 3: Scale the video to fit the new frame
After the change, your widescreen clip will sit in the middle of the tall frame with black bars above and below. To fill the frame, select the clip, open Effect Controls and raise Scale a tiny bit at a time until the picture covers the screen. Then adjust Position so the subject sits where you want them.
This manual method is great when you have only a clip or two, because you decide exactly what stays in the shot. If your subject moves around, it can get tedious, which is where the automatic option helps.
Step 4: Let Auto Reframe Sequence do it for you
For longer videos, Premiere Pro can reframe the whole sequence and follow your subject. With your original sequence selected, open the Sequence menu and scroll down to Auto Reframe Sequence.
Step 5: Pick the target aspect ratio and create
In the Auto Reframe Sequence window, open the Target Aspect Ratio dropdown. It offers Square 1:1, Vertical 4:5, Vertical 9:16, Horizontal 16:9 and Custom. Choose Vertical 9:16 for short-form video. Leave Motion Tracking on Default unless you have a reason to change it, and keep Don't nest clips selected so your own motion adjustments are replaced with the automatic ones.
Click Create. Premiere builds a duplicate sequence, so your original stays untouched. It scales the video and keeps your subject centered throughout the clip.
Tips
- Duplicate first. If you change Sequence Settings by hand, duplicate your sequence beforehand so you keep a widescreen version too.
- Check the whole clip. After Auto Reframe, play the sequence once. If the framing slips on a shot, nudge it in Effect Controls.
- Going the other way? Our guide to turning portrait video into landscape covers the reverse, and fitting a video to the frame helps with black bars.
FAQ
How do I change a sequence to 9:16 in Premiere Pro?
Go to Sequence > Sequence Settings and set the frame size to 1080 horizontal by 1920 vertical.
Can Premiere Pro change the aspect ratio automatically?
Yes. Sequence > Auto Reframe Sequence creates a new sequence in the ratio you pick and keeps your subject centered.
Why does my video have black bars after changing the ratio?
The clip keeps its original shape inside the new frame. Increase Scale in Effect Controls, or use Auto Reframe, to fill the frame.
Want to speed up the rest of your editing too? Browse the Premiere Pro plugins from Adobe Basics.
