Measurement · 2 min read

How do you make a photo smaller for email on a Mac?

By shrinking the long edge, not the quality: reduced to a 2048-pixel long edge, six photos got 78.1% smaller at the median, while quality 80 at full size saved only 21.4%. Measured on October 19, 2026 on a MacBook Pro with sips; 1.46 MB became 256 KB at the median.

How much does reducing the long edge save?

With a 2048-pixel long edge, the six photos got 78.1% smaller at the median on the MacBook Pro on October 19, 2026, and 91.4% smaller at 1280 pixels. 1.46 MB became 256 KB and 107 KB respectively.

Reducing the long edge saves far more than lowering the quality at full size.

Method	Median size	Median saving	Saving range
Original (JPEG, quality 95)	1.46 MB	0%	0%
Full size, quality 80	1.14 MB	21.4%	13.1% to 22.5%
2048-pixel long edge	256 KB	78.1%	73.0% to 94.6%
2048-pixel long edge, quality 80	268 KB	77.0%	71.4% to 94.5%
1280-pixel long edge	107 KB	91.4%	87.4% to 97.6%

Without a quality setting, sips wrote the resized photos slightly smaller than at quality 80.

How much does a lower quality save?

Little, as long as the long edge stays the same: quality 80 at full size saved 21.4% at the median on the MacBook Pro on October 19, 2026. At a 2048-pixel long edge and quality 95, a photo stayed at 488 KB at the median, almost twice the size without a quality setting.

How do you shrink a photo in Preview?

With Tools > Adjust Size and Resample image, then enter a smaller value; Preview shows the new file size at the bottom of the window (Preview User Guide, checked October 19, 2026). In Terminal, sips -Z 2048 shrinks the long edge to 2048 pixels; that is how the 256 KB median on the MacBook Pro on October 19, 2026 came about.

How was this measured?

The measurement covers six JPEG photos on October 19, 2026 on a MacBook Pro with M5 Pro running macOS 27.0.1.

1. Photos: taken from the macOS desktop pictures Sonoma, Sonoma Horizon and Default Aerial and saved with sips as JPEG at quality 95; three crops at 3008 × 3008 pixels, one full picture at 6016 × 6016, and one each at 3840 × 2160 and 4096 × 2160 pixels.
2. Resizing: sips -Z 2048 and sips -Z 1280 for the long edge, -s formatOptions 80 and 95 for the quality (options as described in man sips on macOS 27.0.1, checked October 19, 2026).
3. Analysis: file size in bytes, median and range from minimum to maximum; 1 KB is 1,000 bytes, 1 MB is 1,000,000 bytes.

Photos from a camera or an iPhone, Preview itself and image quality were not measured.