A phone that says storage full always picks the worst moment: you try to take a photo, record a video, or update an app, and the phone refuses. The warning rarely explains what is actually eating the space, so people delete photos at random and the problem returns in a week. This estimator gives you the picture before the warning appears. Enter your counts of photos, videos, and apps with their average sizes, and it shows total gigabytes used, space left, and which category is the biggest user.
The maths is simple multiplication plus one division. Photos times average photo size, plus videos times average video size, plus apps times average app size, gives total megabytes. Dividing by 1,024 turns megabytes into gigabytes. The averages matter more than exact counts: a phone with 2,000 photos at 4 megabytes each holds 8 gigabytes of photos, while 100 videos at 150 megabytes each hold about 15 gigabytes. Video almost always wins, which surprises people who blame their photo library.
Here is a worked example on a 128 gigabyte phone. You have 2,000 photos at 4 megabytes, 100 videos at 150 megabytes, and 60 apps at 200 megabytes. Photos use 8 gigabytes, videos use about 14.6 gigabytes, and apps use about 11.7 gigabytes, for a total near 34.2 gigabytes. That leaves about 93.8 gigabytes free, or roughly 27 percent full. On a 64 gigabyte phone the same collection would fill over half the device before system files, which is why a smaller phone feels full so much sooner.
Video size deserves special attention, because it varies more than any other category. A short clip in standard quality may be 20 megabytes, while a minute of 4K video can pass 350 megabytes. Slow motion, high frame rates, and long recordings multiply that further. If your estimate looks far lower than what the phone reports, video is the first suspect: check the longest clips and any 4K recordings, and consider whether they need to live on the phone or could move to cloud storage or a computer.
Apps are the sneaky category, because the app itself is only part of the story. A messaging app may download as 200 megabytes but grow to several gigabytes with cached photos, videos, and voice messages inside chats. Games with downloaded levels behave the same way. This estimator counts the average app size you enter, so if your apps feel bigger than the number suggests, check the storage settings on your phone, which break down each app into the app itself plus its documents and data.
System files and caches take a share that no estimator can predict exactly. The operating system, preinstalled apps, and temporary files commonly use 10 to 20 gigabytes on a modern phone, before you store a single photo. That is why a 64 gigabyte phone may show only about 50 gigabytes usable on day one. Treat the free space figure here as space for your own files, and subtract a system allowance in your head when you judge whether a phone has room for the next year.
Use the result to act, not just to worry. If videos dominate, back them up and delete the phone copies, starting with duplicates and accidental recordings. If apps dominate, clear caches and remove apps you have not opened in months. If photos dominate, turn on a cloud backup and free up device copies. Recheck every few months, because storage fills quietly: a few photos a day and a weekly video add up to gigabytes per year without any single dramatic download. A quick monthly check takes two minutes and stops the storage full warning from arriving at the worst possible moment.