What size memory card does a dash cam need?

How loop recording uses the card

A dash cam records in short files and, when the card is full, deletes the oldest unprotected file to make room. Card size therefore sets how far back you can go before footage is gone. Clips the camera protects, such as the 30-second clip a Nextbase Series 2 camera saves when its G-sensor detects a bump in Parking Mode, are kept out of the loop. A card that fills up with protected clips has less room for normal driving, so clear them once you have saved what you need.

Read your camera maker's hours figure first

The most reliable number is the one the camera manufacturer publishes for its own models, because only it knows the bitrate its cameras use. Nextbase publishes these figures for its range:

Source: Nextbase FAQs. Nextbase's own support article gives different, lower numbers for some sizes (140 minutes for 32GB without a rear camera, 115 minutes with one, and 9 hours for 256GB), and notes that higher resolution reduces recording time. Treat any single figure as model-dependent and look for the one in your camera's manual.

A worked example from a published bitrate

If your camera's manual does not give hours, you can estimate them from a bitrate. Samsung bases its PRO Endurance ratings on Full HD video recorded at 26 Mbps, which it states as 3.25 MB per second. Dividing card capacity by that rate gives:

Our calculation: capacity in bytes divided by 3.25 million bytes per second, converted to hours. Real figures will be a little lower because a formatted card has slightly less usable space than its label. They will also differ from camera to camera: Nextbase's 16 hours on a 128GB card works out at an average of roughly 18 Mbps, so its cameras evidently record at a lower rate than Samsung's test assumption. Use this table to compare sizes, not to predict your exact camera.

How to choose

1. Check the maximum card size in the manual or listing. The 70mai A510 listing, for instance, states a 256GB maximum.
2. Count your channels. A front and rear camera writes two video streams to one card, so the same card covers fewer hours.
3. Think about how soon you would save footage.If you would only notice a problem a day or two later (a scrape found in a car park, say), you need enough hours to cover that driving.
4. Check the speed rating. Nextbase recommends U3 cards when a rear module is fitted. All three cards below are rated U3 and V30.

Common mistakes

• Buying a card larger than the camera supports.
• Confusing a card's endurance rating (thousands of hours of rewriting over its life) with how many hours it holds at once.
• Forgetting that a rear camera shares the same card.
• Never checking the card. Follow your camera's manual on formatting and check now and then that recent files are actually being saved.

Related pages

• Dash cam features explained
• SanDisk High Endurance vs Samsung PRO Endurance
• Is a rear dash cam worth it?
• Best dash cams

Frequently asked questions

Is a 32GB card enough for a dash cam?

For a front-only camera on short daily trips it can be. Nextbase's FAQ says a 32GB card records up to four hours before looping, or up to two hours with a rear camera module, while its support article gives 140 minutes for 32GB without a rear camera. The gap between those two figures shows how much the model and resolution matter, so check your own camera's number. If you want a day or more of driving on the card, go larger.

Can I just buy the biggest card available?

Only up to the maximum your camera supports. The 70mai A510 listing, for example, states a maximum of 256GB, and Nextbase's support article lists 32GB to 256GB cards. A card above the camera's limit may not be recognised at all.

Do I need a high-endurance card?

A dash cam rewrites the card constantly, which is what endurance cards are rated for. The three cards on this page all quote a recording-endurance figure: up to 10,000 hours of Full HD for the SanDisk High Endurance listing, up to 60,000 hours in the SanDisk MAX Endurance 128GB listing title, and up to 70,080 hours for the Samsung PRO Endurance 128GB. Those figures describe lifetime rewriting, not how much one card holds.

Does a rear camera halve the recording time?

Roughly, on the figures Nextbase publishes. Its FAQ gives up to 16 hours for a 128GB card on a Nextbase dash cam, or up to eight hours with a Rear Cam Module. Other brands may record the rear channel at a lower bitrate, so the reduction can be smaller.