Also asked myself this question today. On my phone and camera, 60fps videos are almost exactly twice the size of 30fps videos, probably because they don't have too much processing power to spare on smart compression and simply double their framerate to remain on the safe side.
Offline compression can yield better results though. For examples, you can look at YouTube's 60fps videos and specifically the sizes of the actual video files behind different quality settings. A tool like youtube-dl
allows you to do that. Here's the output from the tool with a random 60fps Youtube video:
C:\>youtube-dl -F https://www.youtube.com/watch?v=H53QmxZ-rOs
[youtube] H53QmxZ-rOs: Downloading webpage
[youtube] H53QmxZ-rOs: Downloading video info webpage
[info] Available formats for H53QmxZ-rOs:
format code extension resolution note
249 webm audio only tiny 62k , opus @ 50k (48000Hz), 3.23MiB
250 webm audio only tiny 82k , opus @ 70k (48000Hz), 4.41MiB
140 m4a audio only tiny 130k , m4a_dash container, mp4a.40.2@128k (44100Hz), 8.18MiB
251 webm audio only tiny 158k , opus @160k (48000Hz), 8.41MiB
278 webm 256x144 144p 97k , webm container, vp9, 30fps, video only, 5.11MiB
160 mp4 256x144 144p 113k , avc1.4d400c, 30fps, video only, 3.69MiB
242 webm 426x240 240p 228k , vp9, 30fps, video only, 8.69MiB
133 mp4 426x240 240p 281k , avc1.4d4015, 30fps, video only, 7.95MiB
243 webm 640x360 360p 509k , vp9, 30fps, video only, 15.81MiB
134 mp4 640x360 360p 582k , avc1.4d401e, 30fps, video only, 14.79MiB
244 webm 854x480 480p 771k , vp9, 30fps, video only, 26.80MiB
135 mp4 854x480 480p 992k , avc1.4d401f, 30fps, video only, 20.65MiB
247 webm 1280x720 720p 1555k , vp9, 30fps, video only, 52.89MiB
302 webm 1280x720 720p60 2853k , vp9, 60fps, video only, 79.52MiB
248 webm 1920x1080 1080p 2944k , vp9, 30fps, video only, 94.03MiB
298 mp4 1280x720 720p60 3094k , avc1.4d4020, 60fps, video only, 38.61MiB
303 webm 1920x1080 1080p60 4898k , vp9, 60fps, video only, 142.73MiB
136 mp4 1280x720 720p 4910k , avc1.4d401f, 30fps, video only, 62.89MiB
299 mp4 1920x1080 1080p60 5785k , avc1.64002a, 60fps, video only, 123.69MiB
137 mp4 1920x1080 1080p 6930k , avc1.640028, 30fps, video only, 111.05MiB
43 webm 640x360 360p , vp8.0, vorbis@128k, 43.91MiB
18 mp4 640x360 360p 501k , avc1.42001E, mp4a.40.2@ 96k (44100Hz), 31.66MiB
22 mp4 1280x720 720p 1125k , avc1.64001F, mp4a.40.2@192k (44100Hz) (best)
For this video, when compressed with av1, the 60fps FHD video is only 10% larger compared to the 30fps FHD video. But when compressed with vp9, the file size difference is a whopping 60%!
So I guess you can expect 60fps videos sometimes to be up to twice as large, but there are ways to make it have about the same file size with double the framerate, which is pretty neat!