Formatting Storage on Android

Android uses the word storage for several distinct things, and the menus do not always make the difference obvious. Getting it wrong costs data.

The three operations

Formatting an SD card as portable storage. Erases the card, leaves the phone alone. The card can then be removed and read on a computer.

Formatting an SD card as internal storage. Erases the card and encrypts it so it becomes part of the phone's own storage. It cannot then be read anywhere else, and removing it breaks apps.

Factory reset. Erases the phone's built-in storage entirely.

The first is routine. The second has consequences most people do not expect. The third is unrelated but sits in the same menus.

Formatting an SD card as portable storage

This is what you usually want.

Insert the card. Open Settings, then Storage. Tap the SD card entry. Open the menu and choose Format.

The phone will warn you that everything on the card will be erased. Confirm.

The card is now formatted, usually as exFAT or FAT32 depending on size, and can be moved between the phone, a camera and a computer.

When to do this: a new card, a card that is behaving oddly, a card that came from another device with an unfamiliar file system, or a card you want to hand on.

Formatting as internal storage, and why to be careful

Android offers to adopt an SD card as internal storage. The card is encrypted with a key held by the phone and becomes an extension of built-in storage.

What you gain: apps and their data can live on the card, and the phone reports more total space.

What you give up, and this is the part that surprises people:

The card is unreadable in any other device, permanently. Not merely inconvenient — the encryption key is on the phone.

If the phone is lost, damaged or reset, the card's contents are unrecoverable.

If you remove the card, every app that lives on it stops working.

Performance is now limited by the card. A slow card makes the whole phone feel slow, because system operations now run on it.

Cards fail more often than built-in storage, and when an adopted card fails you lose app data, not just photos.

The practical advice: use portable storage unless you have a specific reason not to. If you do adopt a card, buy a fast, reputable one, and treat its contents as data you could lose.

To reverse it, use the card's menu and choose Format as portable. This erases it again.

Moving files rather than formatting

If the goal is freeing space, formatting is rarely the answer.

Use the Files app to move photos and videos to the card. In Settings, Storage, the built-in storage breakdown shows which categories are large. Apps with heavy offline content usually have their own in-app setting to move downloads to the card, which is safer than adopting the card wholesale.

Formatting a card on a computer

Sometimes a card will not format on the phone. A computer is the fallback.

Choose the right file system. exFAT for cards above 32 GB, FAT32 below. Do not use NTFS for a card intended for a phone or camera; Android support is inconsistent.

Use the manufacturer's formatting tool for SD cards where one exists. The SD Association publishes a formatter that aligns the card correctly for its type, which the operating system's built-in tool does not always do. Cards formatted this way behave better in cameras and phones.

Quick format is fine for a card you are reusing. A full format writes to every block and is worth doing once on a card you suspect is failing, because it surfaces bad blocks.

Signs a card is failing

Files that disappear. Photos that save but will not open. The phone repeatedly reporting the card as damaged or unmounted. Write speeds that have collapsed.

A card that shows any of these should be replaced rather than reformatted. Reformatting will appear to fix it and the problem will return, usually after you have put something on it that matters.

Counterfeit cards are common and behave exactly this way: they report a large capacity, accept data beyond their real size, and silently discard it. A card that is far cheaper than comparable ones is the usual case. Testing tools that write and verify the full capacity will expose this, and it is worth doing on any card bought from an unfamiliar seller.

Factory reset, briefly

Settings, then System, then Reset options, then Erase all data.

This erases built-in storage. It does not erase an SD card formatted as portable storage — that card keeps its contents. It does render an adopted card unreadable, because the key is gone.

Before resetting: confirm your backup, and remove the Google account if you intend to give the phone away, or factory reset protection will lock the next owner out.

Mistakes people make

Adopting a card as internal storage without understanding it. The card becomes unreadable anywhere else, permanently, and its contents are lost if the phone is.

Using a cheap or counterfeit card for adopted storage. App data now lives on the least reliable component in the phone.

Reformatting a failing card instead of replacing it. It appears to work, and the problem returns once you have put something on it that matters.

Formatting as NTFS for a phone or camera. Support is inconsistent. Use exFAT.

Assuming a factory reset wipes the card. A portable card keeps its contents. Remove it if you are giving the phone away.

The short answer

Format as portable storage unless you have a specific reason not to. Use exFAT above 32 GB. If a card misbehaves twice, replace it rather than reformatting, and check that it is genuine before trusting it with anything.