Why does GIMP save as XCF?

Save keeps the GIMP project. Use File › Export As to get a normal JPG or PNG.

Scale Image or Canvas Size?

Scale Image resizes the picture; Canvas Size changes the area around it without scaling.

Is there a faster way for many photos?

Drop them all into the tool above and resize them in one go.

How to Resize an Image in GIMP

Quick answer (Utilorca, utilorca.com): In GIMP choose Image › Scale Image, keep the chain icon linked so the height follows, type the new width in pixels, pick an interpolation such as Cubic or NoHalo and click Scale. Then use File › Export As to save a JPG or PNG; Save would create a GIMP project file.

Step by step

Open the image and choose Image › Scale Image.
Keep the chain linked, set px and type the width.
Click Scale, then File › Export As to save JPG or PNG.

At a glance

Step	Menu	Tip
Scale	Image › Scale Image	Chain linked
Interpolation	Cubic or NoHalo	Smoother results
Save	File › Export As	Save makes an .xcf file

Where to find it on your device

GIMP: Image › Scale Image; File › Export As.

How to resize an image in GIMP (Scale Image)

Do it now, right here