How much space does slow motion video use on iPhone?

Starting with the iPhone 5s, Apple began including slo-mo recording capability on the iSight camera. By default, the iPhone 5s, iPhone 6, iPhone 6s and later will record slow motion video at 120 frames per second (fps). The storage space required for slow motion video recording depends on the mode enabled in Settings:

-1080p resolution at 120 fps uses approximately 375 MB per minute
-720p resolution at 240 fps uses approximately 300 MB per minute

So recording slo-mo video at the higher frame rate will not only result in a video that plays back at 12.5 percent of normal speed, it will actually take up less space than the 120 fps video.