Dashcam Loop Recording Calculator

Why your dashcam quietly deletes its own footage

A dashcam never stops recording, but its memory card is finite — so every dashcam records in a loop. When the card fills up, the oldest clip is erased to make room for the newest one. That is normal behavior, not a fault, and it is exactly why the card size you buy decides how far back in time your evidence goes.

How the loop math works

Video size is set by bitrate, not by the length of your drive. A 1080p dashcam at about 10 Mbps writes roughly 4.5 GB per hour; 2K at 20 Mbps doubles that to about 9 GB per hour; 4K at 35 Mbps lands near 15.8 GB per hour. Add a rear camera and the numbers double again. Divide your card's size by the gigabytes per hour and you get the loop length: the hours of driving history the card holds before it starts overwriting. (Bitrate x 0.45 gives GB per hour per camera — 10 Mbps x 0.45 = 4.5.)

Worked example

Take a 128 GB card in a front-only 1080p dashcam at 10 Mbps. Each hour needs about 4.5 GB, so 128 / 4.5 = 28.4 hours of loop recording — roughly a full week of commuting before the oldest footage is replaced. Switch that same card to a 4K front+rear setup (35 Mbps x 2 cameras = 31.5 GB per hour) and the loop shrinks to just 2.0 hours: a single long drive can erase the morning's footage by evening.

Practical tips

Buy the biggest card your dashcam supports — 128 GB is the sweet spot for most 1080p drivers, 256 GB for 4K or dual-channel setups. Use a high-endurance card made for constant rewriting; ordinary cards wear out fast in a dashcam. Format the card in the dashcam itself every month or two, and if an incident matters, pull the card immediately — the loop will not wait for you.