How much hard-drive capacity do you need?

Buying a hard drive often starts with a familiar problem: your computer is full, your photos are scattered across several disks, or you’ve finally decided to give your files a proper backup. You want enough space to stop worrying about it for a while, without paying for a huge drive you’ll never fill.

The right size depends on what your data actually consists of. Years of documents can fit into a small corner of a drive; a few video projects can take over the rest. Start by checking how much space your files use now, including anything you’ll move over from other disks or cloud storage. Then think about what you’re likely to add over the next few years.

The ranges below give you somewhere to start shopping. If your data already fills most of a suggested size, move up a size. You want room to use the drive, not just squeeze everything onto it.

Documents and everyday files

1–2 TB is usually plenty for documents, spreadsheets, music, and a modest collection of photos. If all your folders add up to a few hundred gigabytes and you’ve been collecting them for years, you probably don’t need a much bigger disk.

I’d lean toward 2 TB if you’re also gathering files from an old computer or keeping home videos. Once you’re approaching a terabyte of files, 2–4 TB gives you more breathing room. There’s no great saving in buying a smaller drive if you’ll need to replace it soon.

Photos and home videos

For family photos, phone pictures, and short home videos, 2–4 TB is a good starting point. The videos deserve a closer look: they can account for much of the space even when your photo app makes them look like a small part of the collection.

Photography as a hobby changes the calculation. Keeping RAW files—the original image data from your camera—alongside edited pictures means saving several versions of your work. 4–8 TB suits a growing camera library, while 8–16 TB makes more sense if you’ve already accumulated several terabytes and still shoot regularly.

Movies, TV, and a media server

4–8 TB can hold a modest media collection, but a library that grows every week will soon make 8–16 TB appealing. If you keep large disc copies or have years of movies and TV shows already on disk, 16–24 TB and larger drives are worth looking at.

This is one use case where counting files tells you very little. Two copies of the same movie can be very different sizes, so promises about how many movies a drive holds aren’t much help. Your existing folders and the amount you’ve added over the past year will give you a much better estimate.

Video projects

Original footage tends to stay long after the finished video is exported. If you want to keep it all, size the drive for complete projects, including the footage and finished work.

4–8 TB is a reasonable archive size for occasional projects. Regular shooting can make 8–16 TB a more comfortable choice, and a substantial archive may need 16–24 TB per drive or several disks. Measure a few of your completed projects before buying. “4K” alone doesn’t tell you how big the files will be: recording settings and compression matter too.

Backing up a computer

A backup drive needs space for more than one copy of today’s files. Keeping older versions is what lets you recover a document you changed last week or a folder you deleted before noticing it was missing.

For a laptop with a few hundred gigabytes of files, 2–4 TB is a sensible backup size. A desktop with a large photo collection or other files you need to protect may need 4–8 TB. Add several household computers or external drives to the job and 8–16 TB becomes easier to justify.

Your backup software also matters. For Time Machine, Apple recommends a disk with at least twice the storage capacity of your Mac. Other tools keep history differently, so check how much they’re set to retain. If you’re backing up a NAS, work from the amount of data you actually need to copy, with room for history and growth.

A home NAS

A NAS shares storage over your home network, often combining several drives in one box. 4–8 TB per drive is a useful starting range for household files and photos. A media library and backups from several computers can make 8–16 TB per drive a better fit. When you’ve already built a large collection, 16–24 TB or more may be worth the cost, especially in a box with only two drive bays.

The capacity on the labels isn’t necessarily the space you’ll have for files. With two 8 TB drives set up as a mirror, both disks store the same data. You get roughly one 8 TB drive’s worth of space, with a little more used by the system. Other RAID layouts divide up space differently; Synology’s RAID calculator can help you see how a proposed set of drives adds up.

Allow for a separate backup in the budget. A mirror can keep your NAS running after one disk fails, but it also copies an accidental deletion. Before ordering, check that the NAS supports the drives and capacities you’ve chosen.

How much spare room to buy

Think about the next two or three years, using your recent habits as a guide. With 3 TB of files and roughly another terabyte arriving each year, I’d shop for an 8 TB drive. A 4 TB model would be nearly full after the first year. If your folders barely grow, you don’t need to make the same jump.

Leave some space beyond that estimate for a new project or a collection you hadn’t planned to keep. You don’t need a precise percentage; you need enough room that adding something substantial won’t immediately mean buying another disk.

Once you’ve settled on a range, compare the purchase price as well as the price per terabyte. Extra capacity is worth paying for when you’ll use it or it saves you replacing a drive. If it’s likely to sit empty, a second copy of your important files is a better use of the money.