Dash Cam Loop Recording Explained
October 17, 2026 · 12 min read
You just found out your dash cam only keeps a few hours of video, and you want to know what happens to the rest. Maybe someone clipped your mirror last week and the clip was already gone. This guide answers what is loop recording on a dash cam, how long your footage survives on your card, and how to make sure the one clip you need never gets erased.
Updated — first edition of this guide
Quick answer
Loop recording on a dash cam saves video in short 1- to 3-minute clips and, once the memory card is full, records over the oldest clip that is not locked, so a 128 GB card at a typical 1080p bitrate of 12 Mbps holds about 22 hours of driving before the first clip is overwritten.
Who this guide is for
This guide is for anyone who owns a dash cam, or is about to buy one, and wants to know how long the footage lasts. You do not need to know anything about memory cards to follow it.
This is for you if
- You went to pull a clip and found it had already been recorded over
- You are choosing a microSD card and want to know which size to get
- Your camera keeps saying “card full” or “please format”
Look elsewhere if
- You want to know whether recording is allowed where you drive: read are dash cams legal in your state?
- You need to recover footage that has already been overwritten. Loop recording replaces the data, and this guide cannot bring it back
How this guide was researched
Every figure here comes from manufacturer documentation, a card standard, or simple arithmetic you can repeat yourself.
Our research method
- Cedar Buy read dash cam support pages and manuals from Nextbase, Garmin, VIOFO and BlackVue, the SD Association’s guidance on card formatting, and SanDisk’s published endurance ratings, in October 2026.
- Recording hours in the table are calculated from bitrate, not copied from one brand’s chart, so they apply to any camera once you know its bitrate.
- The calculation was checked against BlackVue’s own published recording times, and the two agree within about 2%.
- Specifications come from manufacturer documentation. Cedar Buy does not physically test products — see our editorial policy.
What is loop recording on a dash cam?
Loop recording means the camera never stops to ask for space. It records in short clips, and when the card fills up it deletes the oldest unlocked clip and writes the new one in its place. Nextbase’s support guide describes exactly this: continuous recording that overwrites the oldest unprotected footage once the card is full.
The clips are short on purpose, usually 1, 2 or 3 minutes, and you can set the length in most cameras’ menus. A short clip means the camera only throws away a minute or so of old video at a time. It also means a clip you want to share is small enough to send from your phone.
How long before footage is overwritten
Your footage lasts as many hours of driving as your card holds, and no longer. That window is set by three things: card size, how much data the camera writes per second (its bitrate), and how many cameras are recording.
Count driving hours, not calendar days. A camera that only runs while the engine is on will keep 22 hours of footage for about two weeks if you drive 90 minutes a day. A camera in parking mode (recording while the car is off) eats into that same space, so the window can shrink to a day or two.
Locked files shrink it too. Every locked clip takes space the loop cannot use, as Nextbase warns: a build-up of protected files shortens recording time.
Card size vs recording hours
A 128 GB card holds about 22 hours of single-camera 1080p video, but only about 4 hours of 4K front plus 1080p rear. The table shows the rest. Find your setting, then read across to your card size.
| Recording setting | Typical total bitrate | 64 GB | 128 GB | 256 GB | 512 GB |
|---|---|---|---|---|---|
| 1080p, front only | 12 Mbps | 11 hours | 22 hours | 45 hours | 90 hours |
| 1080p front + 1080p rear | 24 Mbps | 5.6 hours | 11 hours | 22 hours | 45 hours |
| 1440p (2K), front only | 25 Mbps | 5.4 hours | 11 hours | 22 hours | 43 hours |
| 4K, front only | 50 Mbps | 2.7 hours | 5.4 hours | 11 hours | 22 hours |
| 4K front + 1080p rear | 66 Mbps | 2.0 hours | 4.1 hours | 8.2 hours | 16 hours |
Bitrate is the number of megabits of video the camera writes every second, shown as Mbps. The table uses this formula: card size in GB × 0.95 × 8,000 ÷ bitrate in Mbps ÷ 3,600 = hours. The 0.95 allows for space the card’s file system uses, so the result is an estimate, not a measurement.
The bitrates are typical figures for each setting, taken from published dash cam specifications. As a check, BlackVue states that its dual-camera Full HD DR590W-2CH records over 22 hours on a 256 GB card at its highest quality, which matches the second row. Your own camera’s bitrate is in its manual or spec sheet. Plug it into the formula and you have your exact window.
What the table does not show
These hours assume nothing is locked and parking mode is off. Every locked clip and every hour of parking footage comes out of the same space, so your real window is shorter than the table if you drive on rough roads or record while parked.
Locked files and how they survive the loop
A locked file is a clip the camera moves out of the loop so it is not recorded over. Cameras lock a clip in two ways: automatically when the G-sensor (a motion sensor that feels sudden jolts) detects an impact, or manually when you press the camera’s lock or save button.
Most cameras keep locked clips in their own folder. Garmin’s Dash Cam Mini manual lists separate folders for incident videos and manually saved videos, and says only the unsaved folder gets overwritten when its space runs out.
Locked clips are not safe forever, though. Nextbase notes that protected files can be overwritten once the protected-file space limit is reached. Other cameras do the opposite and stop recording when the card fills with locked clips. Either way, copy any clip you need to your phone or computer the same day.
Turn the G-sensor sensitivity down if your camera locks clips on every pothole. On a high setting, a bumpy commute can fill the locked folder with clips you will never watch.
Formatting: how often and why
Format your dash cam’s card about once a month, and more often if you drive every day. VIOFO’s support center gives that once-a-month guidance, because constant writing and rewriting puts stress on the card. Formatting wipes everything and rebuilds the card’s file system (the index that tracks where each clip is stored), which clears out errors before they turn into a missing clip.
Here is how to format an SD card for a dash cam:
- Copy off any clip you want to keep. Formatting deletes every file, locked ones included.
- Format in the camera first. Look for Format in the camera’s settings menu or app. The camera writes the exact layout it expects.
- If the camera refuses the card or keeps showing errors, format it on a computer with the free SD Memory Card Formatter from the SD Association. VIOFO also advises against the Quick Format option on a computer.
- Put the card back in the camera and let it record for a minute to confirm it works.
The file system matters. The SD Association’s formatter picks FAT32 or exFAT based on card capacity. Cards up to 32 GB (SDHC) use FAT32, and cards of 64 GB and up (SDXC) use exFAT. Some cameras want FAT32 even on larger cards, which is one more reason to format in the camera first.
Endurance cards vs normal cards
Buy an endurance card. A dash cam writes to its card every second it is on, and a high-endurance card is built and rated for that constant rewriting, while most standard cards publish no recording-hours rating at all.
A published endurance rating
Look for a rating in hours of recording. SanDisk rates its High Endurance microSD at up to 10,000 hours of Full HD recording for the 128 GB card and 20,000 hours for the 256 GB card, with fewer hours at 4K. A card with no rating gives you nothing to compare.
V30 or U3 speed class
V30 (Video Speed Class 30) promises a sustained write speed of 30 MB/s, and U3 promises the same. VIOFO recommends a U3 card for 4K recording. That speed is far above what any setting in the table needs, so V30 is enough for every dash cam.
Enough capacity for your window
VIOFO names 64 GB as the minimum it recommends for a dash cam. Get 128 GB for a single 1080p or 2K camera, and 256 GB for 4K or any front-and-rear setup. Check your camera’s maximum supported card size first.
Read speed barely matters
The big “up to 100 MB/s” on the package is read speed, which only affects how fast you copy clips to a computer. It does nothing for recording. Ignore it and compare endurance ratings instead.
Key terms, explained
These four terms show up in every dash cam manual, and each one changes how long your footage lasts.
Plain-language definitions
- Bitrate
- The amount of video data a camera writes each second, measured in megabits per second (Mbps). Dash cams typically record 1080p at around 12 Mbps and 4K at around 50 Mbps, and a higher bitrate fills a card faster.
- Locked file (event file)
- A clip the dash cam has protected from loop recording, either automatically after the G-sensor detects an impact or because you pressed the lock button. Locked files take space away from normal recording until you delete them or format the card.
- Endurance rating
- A card maker’s figure for how many hours of video a card can record and rewrite before it wears out. It is quoted at Full HD, so the real figure is lower for 4K.
- exFAT and FAT32
- Two file systems, the filing method a card uses to track its data. Under SD Association standards, cards up to 32 GB use FAT32 and cards of 64 GB or more use exFAT.
Mistakes that cost people footage
The most expensive mistake is waiting days to save a clip, and finding the loop has already recorded over it.
- Waiting to copy off an important clipOn a 64 GB card at 4K, the window is under 3 hours of driving. Press the lock button at the scene, then copy the clip to your phone the same day.
- Using the card that came in the boxBundled cards are often small and carry no endurance rating. Swap it for a rated high-endurance card before you rely on the camera.
- Never formatting the cardErrors build up over months of rewriting, and the first sign can be a clip that will not play. Format monthly, in the camera.
- Leaving G-sensor sensitivity on highEvery bump locks a clip, the locked folder fills, and normal recording space shrinks. Set it to low or medium for daily driving.
Frequently asked questions
Does loop recording delete accident footage?
Not if the clip is locked. When the G-sensor feels an impact, or you press the lock button, the camera moves that clip out of the loop so normal recording cannot overwrite it. Some cameras will still overwrite the oldest locked clips once the locked-file space is full, and others stop recording instead. Copy any accident clip to your phone or computer the same day to be safe.
Can I turn off loop recording on my dash cam?
Most dash cams let you switch loop recording off in the settings menu. The catch is that the camera then stops recording when the card is full, so a drive late in the week may not be recorded at all. For almost everyone, leaving loop recording on and locking the clips that matter is the safer setup.
How do I format an SD card for a dash cam?
Format it inside the dash cam first, using the Format option in the camera’s menu or app, after copying off any clips you want to keep. The camera writes the layout it expects. If the camera rejects the card, format it on a computer with the free SD Memory Card Formatter from the SD Association, then put it back and confirm the camera records.
What size SD card do I need for a dash cam?
Get 128 GB for a single camera recording 1080p or 2K, which holds roughly 11 to 22 hours of driving. Get 256 GB for 4K or a front-and-rear camera, which holds roughly 8 to 22 hours depending on bitrate. VIOFO names 64 GB as its recommended minimum. Always check the largest card your camera supports before you buy.
Why does my dash cam say the card is full when loop recording is on?
Usually the card has filled with locked clips, which loop recording is not allowed to overwrite. Copy off the clips you need, then format the card in the camera. If the warning comes back quickly, turn the G-sensor sensitivity down so bumps stop locking clips. A worn-out or failing card can show the same message, so replace it if formatting does not help.
What to do next
Check your camera’s bitrate, use the table to pick a card that holds at least a week of your driving, and put formatting on your calendar once a month.
If you are setting up a new camera, the card is only half the job. Mount position decides what the camera actually sees, so read where to place a dash cam before you stick the mount to the glass. Then lock a test clip, copy it to your phone, and make sure you know how to do it before you need it. That is Cedar Buy’s whole recommendation: a rated endurance card, a monthly format, and the habit of saving clips the same day.
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