How Many Hours Fit on a Card?
It depends on your camera's bitrate, not just the card's capacity. File size scales directly with bitrate: roughly 6.75 GB per hour at a low ~15 Mbps bitrate, 13.5 GB per hour at a mid ~30 Mbps bitrate, and 22.5 GB per hour at a high ~50 Mbps bitrate. Divide your card's capacity by the GB/hour figure that matches your camera's actual bitrate to estimate retained hours before loop recording starts overwriting the oldest footage.
Estimated hours by card size and bitrate
| Bitrate band | GB per hour | 64GB card | 128GB card | 256GB card |
|---|---|---|---|---|
| ~15 Mbps (low band) | ~6.75 GB | ~9.5 hrs | ~19 hrs | ~38 hrs |
| ~30 Mbps (mid band) | ~13.5 GB | ~4.7 hrs | ~9.5 hrs | ~19 hrs |
| ~50 Mbps (high band) | ~22.5 GB | ~2.8 hrs | ~5.7 hrs | ~11.4 hrs |
Figures are single-channel (front-only) estimates from bitrate-to-filesize math (Mbps × 3600 ÷ 8 ÷ 1000); a 2-channel front+rear camera roughly halves these hours for the same card.
Why bitrate, and not just capacity, sets your retention window
A bigger card always buys you more retained hours proportionally, but at a high bitrate that gain is smaller in absolute hours than the same card at a low bitrate. If long retention matters more to you than maximum detail, a mid-bitrate camera on a large card may retain more usable driving history than a high-bitrate camera on the same card. See why bitrate matters for the quality side of that tradeoff, and use only an endurance-rated card regardless of size.
Frequently Asked Questions
It depends on bitrate, not just capacity: roughly 19 hours at a low ~15 Mbps bitrate, about 9.5 hours at a mid ~30 Mbps bitrate, or about 5.7 hours at a high ~50 Mbps bitrate, before loop recording begins overwriting the oldest footage.
Roughly — a 2-channel camera records two simultaneous streams, so total combined data roughly doubles versus a single front-only stream at the same per-camera bitrate, which roughly halves the retained hours for a given card size.
Loop recording keeps the camera always ready to capture the most recent driving, rather than stopping recording once storage fills — the tradeoff is that older footage is deleted to make room unless a clip is manually protected/locked (e.g., via impact detection).
Yes, proportionally, for the same bitrate — capacity and retained hours scale linearly. Bitrate, not capacity, is what determines the GB-per-hour rate you're dividing that capacity by.