Free Tool
Dash Cam Storage Calculator
How many hours fits on the card — and how long before loop recording overwrites the clip you needed.
Estimates based on typical H.265 bitrates. Actual file sizes vary by codec (H.264 runs roughly 1.5× larger than H.265 at equal quality), scene complexity, and whether audio is recorded. Cards also reserve some capacity, so usable space is around 93% of the labelled size — that is accounted for here.
Why resolution matters less than you think
Storage is consumed by bitrate, not resolution. A 4K camera recording at a conservative 24 Mbps produces smaller files than a 1440p camera set to 30 Mbps. Manufacturers rarely publish bitrate, which is why two cameras with identical specs on paper can fill the same card at very different rates.
Adding channels multiplies consumption almost linearly. A front-and-rear 4K setup burns through storage roughly twice as fast as front-only — the single most common reason people find their incident was already overwritten.
Loop recording and the clip you actually need
Dash cams record in a loop, overwriting the oldest footage once the card is full. The number that matters is not total capacity but how many days of your driving fit before overwrite. If you only discover a scratch or a hit-and-run a week later, a card holding three days of footage is no help.
Two practical consequences:
- Parking mode changes the maths. Motion or impact-triggered parking recording adds hours you did not plan for. If you park on a street, assume significantly more consumption than the driving-only figure above.
- Protected files eat capacity permanently. Impact-locked clips are excluded from the loop, so a camera that locks aggressively slowly shrinks its own usable space until you clear them.
Cards wear out
Dash cams write continuously, which is exactly the workload consumer memory cards handle worst. Use a high-endurance card rated for video surveillance, and expect to replace it roughly annually in daily use. A failed card usually fails silently — the camera appears to be recording and is not.
Shopping for one? See our dash cam guides and data studies for measured prices and picks.
Recording hours by card size and bitrate
What the calculator produces, written out. Hours are of continuous recording; a dash cam loops and overwrites the oldest footage, so these are the windows of history the card holds rather than a limit on how long it runs.
| Mode (total bitrate) | 32 GB | 64 GB | 128 GB | 256 GB | 512 GB |
|---|---|---|---|---|---|
| 1080p 30fps, front only8 Mbps | 8.3 hr | 16.5 hr | 33.1 hr | 66.1 hr | 132.3 hr |
| 1440p 30fps, front + rear28 Mbps | 2.4 hr | 4.7 hr | 9.4 hr | 18.9 hr | 37.8 hr |
| 4K 30fps, front only24 Mbps | 2.8 hr | 5.5 hr | 11.0 hr | 22.0 hr | 44.1 hr |
| 4K 30fps, front + rear48 Mbps | 1.4 hr | 2.8 hr | 5.5 hr | 11.0 hr | 22.0 hr |
| 4K 30fps, front + rear + interior72 Mbps | 55 min | 1.8 hr | 3.7 hr | 7.3 hr | 14.7 hr |
| 4K 60fps, front + rear80 Mbps | 50 min | 1.7 hr | 3.3 hr | 6.6 hr | 13.2 hr |
Model: usable capacity is about 93% of the printed size, and each channel adds its own bitrate — a front-and-rear 4K cam writes roughly double a front-only one. Bitrates are typical published figures; a specific model may differ by a few Mbps.
A worked example
A 4K front-and-rear cam writes about 48 Mbps in total. On a 128 GB card that is 5.5 hr of footage — so if you drive an hour a day, the card holds roughly 6 days of history before it starts overwriting. Drop to 1080p front-only and the same card holds 33.1 hr.
That is the practical reason resolution matters less than buyers expect: doubling resolution halves how far back you can look, and for an insurance dispute the footage you need is usually from this week, not last month.
FAQ
Why is usable capacity less than the printed size? Cards reserve space for the filesystem and for wear levelling. About 93% is available in practice.
Does a bigger card make the camera record longer? No — loop recording never stops. A bigger card widens the window of history you keep.
What size should I buy? Enough to cover the gap between an incident and when you notice it. A week of your own driving is a sensible floor, which for most 4K front-and-rear setups means 128 GB or more.
Shopping for one? See our dash cam guides for picks and measured prices.