SD Card for a Security Camera: Which Size to Buy

For most home setups, a 64GB or 128GB card is the sensible choice for a security camera, as long as your camera's manual says it accepts that size. Pick the capacity from how many days of loop recording you want to keep, then check the largest card your model is rated for. A bigger card than the camera supports can fail to mount or format, and a bigger card than you need just stores older footage you will never watch.

This guide shows how to turn "days of footage" into a card size with simple arithmetic, what each common size holds, how to read your camera's card limit, and the cases where a larger card is wasted money. If you are weighing the very largest cards, we cover that separately in the 1TB card guide.

How loop recording decides what size you need

A camera with a memory card records continuously or on motion, and when the card fills up it overwrites the oldest footage. That is loop recording. So the card never "runs out" in the sense of stopping; what you are really choosing is how far back you can look before the oldest clips are erased.

Two things control that window:

• How much data the camera writes per hour. This depends on the video bitrate the camera uses, which depends on resolution, scene activity and the quality setting.
• How much of the day it records. Continuous recording fills the card fastest. Motion-only recording can stretch the same card many times further in a quiet place.

Your camera does not publish a fixed gigabytes-per-day number for every scene, so treat any figure below as a worked example, not a promise. Your model's manual or its storage screen in the app is the real source.

The simple arithmetic: bitrate to days

Video is measured in megabits per second (Mbps). One hour of video at 1 Mbps is roughly 0.45GB, and a full 24 hours is roughly 10.8GB. Double the bitrate and you double the storage.

Here is a worked example using two assumed bitrates. These are illustrations for the arithmetic, not specifications of any camera:

Card label	Assumed 1 Mbps, 24h continuous	Assumed 2 Mbps, 24h continuous
32GB	about 3 days	about 1.5 days
64GB	about 6 days	about 3 days
128GB	about 12 days	about 6 days
256GB	about 24 days	about 12 days

Two adjustments make real life a little shorter than the table. First, a card's printed capacity is more than the space you can actually use, because the file system and the camera's own bookkeeping take some. Second, the camera may also store audio and event markers. So round the days down, not up.

To use this for your own camera, find its bitrate. Some apps show it in the video quality or stream settings, and some manuals list it. If neither does, record one hour, then check how much space the card reports as used. Multiply by 24 for a continuous day.

What each size realistically gives you

32GB: a short window, fine for a spare camera

A 32GB SD card is the entry size. Under continuous recording the table above shows only a day or two, which is enough to review "what happened last night" and not much more. It is a good match for an indoor camera that records only on motion, a spare camera on a low-traffic corner, or a trial run while you learn the app.

If you put a 32GB microSD card in a camera that records around the clock and you are away for a weekend, it may well have overwritten Friday by the time you return on Monday.

64GB: the quiet middle

A 64GB card roughly doubles that window. It suits a small apartment or a single-room camera on motion recording, where the camera writes only when something moves. How many days it really covers depends on how often that room has motion.

128GB: the best value for most people

A 128GB microSD card is a good middle choice for a front door, driveway or storefront camera. In continuous mode the table shows about 6 to 12 days depending on bitrate, and with motion recording the window can stretch further in a quiet place. It gives margin for the usable-space loss, for a busier scene, and for a higher quality setting without forcing you to give up days of history.

256GB: only if your camera supports it and you need the history

A 256GB microSD card makes sense when you record continuously at a higher quality, run a busy scene such as a street frontage, or want weeks of history because you travel often. The catch is the card limit. Some cameras are rated only up to a smaller size, so confirm the supported maximum in your manual before you buy. If your model accepts 256GB, the extra history may be worth the price.

Match the card to the camera's stated limit

Every camera lists the largest card it accepts, in its manual, on the box or on the product page. That is the number that matters, not what the card can theoretically do. Here is how to handle it:

1. Read the limit as a ceiling, not a target. If the manual says the camera accepts cards up to a stated size, anything at or below that should work, and anything above it may not be recognized, may refuse to format, or may be seen with the wrong size.
2. Check the card family. Cards up to 32GB are labeled SDHC, and cards from 64GB up are labeled SDXC. A camera that only supports the older SDHC family can read 32GB and smaller but not larger. When a listing says "SDXC memory card for camera," it is telling you the card uses the newer format, which some cameras read and some cannot. If the manual only names a size and not a format, buy a card at or below that size and test it right away.
3. Format it in the camera. Insert the card, format it from the camera's storage menu in the app, and wait until it shows the capacity. Formatting in a computer can leave a file system the camera dislikes. If the card does not show up afterward, our guide on why a camera is not recording to the SD card walks through the usual causes in order.
4. Test before you trust it. Record for a few minutes, trigger motion, then play the clip back from the card in the app. Do this on the day you install it, not the day you need the footage.

If you are unsure about the terms on the packaging, TF card and microSD card are essentially the same format under different names. TF (TransFlash) was the original name of the microSD format, so you can use either word when searching.

Speed and endurance matter as much as size

Capacity is only half the choice. A camera writes to the card all day, which is very different from a phone that saves a photo now and then. Two points:

• Pick a card built for constant writing. Standard cards are designed for occasional use and can wear out or corrupt when recorded to around the clock. Cards sold as high-endurance are made for continuous video. We compare them in our high-endurance card guide.
• Check the speed class listed for your camera. If the manual names a minimum speed class, follow it. A card that is too slow can produce gaps or stutter in the recording.

A smaller high-endurance card can serve a camera better than a larger standard one.

When a bigger card is wasted

Going up in size feels safe, but it does not always help. A bigger card is wasted in these cases:

• The camera records only on motion in a quiet place. If the card is barely half used after a month, doubling it just adds empty space.
• You never look back further than a few days. If you check the app when an alert arrives, a week of history is plenty.
• Your model's limit is lower than the card. A larger card that the camera cannot read is not a safety margin; it is an error message.
• You already back up elsewhere. If clips are copied to a cloud service or a recorder, the card is only a buffer.
• The scene never changes. A bedroom with few events fills slowly, so even a small card lasts.

In these cases, a right-sized card is enough.

When a bigger card is worth it

There are also clear cases where stepping up pays off:

• Continuous recording at the highest quality setting. This fills the card quickly, so bigger buys real days.
• A busy scene. Lots of movement means lots of motion triggers, which makes a "motion only" camera behave more like a continuous one.
• You travel and need weeks of history. If you are away for long stretches and only check afterward, the longer window is the whole point.
• The camera is hard to reach. If swapping the card means a ladder or a trip across town, buy larger and rarely touch it.

If your camera has a mobile-network (SIM) option, check its manual for how recording and the card work together, and see how a 4G camera uses a SIM and a memory card before choosing a size.

A quick way to choose

Use the arithmetic above with your desired number of days, add margin because usable space is less than the label, round up to the next standard size, then check it against the camera's stated limit. If it is above the limit, take the largest supported size and accept a shorter window, or switch to motion recording.

If your needs are much larger than a card can sensibly hold, such as many cameras and weeks of continuous video, a recorder with a hard drive is the better fit. Our storage calculation guide shows how to size that.

Frequently asked questions

What is the best SD card for camera loop recording?

For most homes, a 64GB or 128GB high-endurance card at or below your camera's stated limit is the best balance. The window depends on your scene and settings, so use the arithmetic above to check it.

Is a 32GB SD card enough for a security camera?

It is enough if the camera records on motion or you only need a day or two of history. With continuous recording, a 32GB card can overwrite itself within a couple of days, as the table shows, so choose a bigger one if you travel.

Is 128GB or 256GB better for a camera?

Choose 128GB unless you record continuously at a high quality setting, watch a busy scene or want weeks of history. Also confirm in your manual that your camera accepts 256GB, because some models stop at a smaller size.

Will a larger card than the manual lists work?

Sometimes it is recognized, but you cannot rely on it. The camera may fail to mount, refuse to format, or show the wrong size. Use a card at or below the stated limit, and test it by playing back a recording.

Does SDXC work in every camera?

No. SDXC is the newer format used for cards above 32GB, and older cameras may only read the SDHC family. Check the manual for the maximum card size and format before buying.

Why does my footage cover fewer days than the table says?

The card has less usable space than its label, the bitrate may be higher than assumed, and busy scenes trigger more recording. Measure your own camera for an hour and recalculate.