SD Card Recording Time Calculator
Knowing how long a camera can record before its SD card fills helps you choose storage that fits your security setup. The SD Card Recording Time Calculator estimates continuous recording time using card capacity, average video bitrate, usable storage, and the number of streams sharing the card.
The result is an estimate in hours. Actual recording time can differ because cameras use storage in different ways and video bitrates can change with motion, image detail, audio, and recording settings.
What the SD Card Recording Time Calculator does
The calculator estimates how much continuous footage an SD card can hold before its usable space is full. It combines the storage available on the card with the amount of data the camera writes each second.
For a camera using loop recording, the result is an estimate of the footage retention window: how much footage may be stored before the oldest recordings begin to be overwritten. For a device that stops recording when its card is full, it estimates the time until recording stops.
The calculation assumes that each stream records continuously at the average bitrate you enter. If multiple streams share the card, it also assumes they all use that same average bitrate. The defaults are illustrative, so use your camera’s settings or measured storage usage when you have them.
How to use the SD Card Recording Time Calculator
Enter the following information to estimate recording time:
- SD card capacity (GB): Enter the card’s advertised capacity in gigabytes. For example, enter 128 for a 128 GB card.
- Bitrate per stream (Mbps): Enter the average recording bitrate for one video stream in megabits per second. Include audio in this figure if the camera records audio and it is not already included in the reported bitrate.
- Usable storage (%): Enter the percentage of the card available for recordings after allowing for formatting, system files, and other storage overhead. For example, 90% is an illustrative assumption, not a guaranteed amount of usable space.
- Number of streams sharing the card: Enter how many video streams record continuously to that same card. Use 1 for a single stream.
The Recording Time result appears in hours to two decimal places. If you want to compare storage options, change the card capacity while keeping the other inputs the same. You can also compare different recording settings by changing the average bitrate.
Check whether your camera reports bitrate in Mbps, rather than megabytes per second. The two units are different: one byte contains eight bits. Entering a value in the wrong unit can make the estimate substantially inaccurate.
How the SD Card Recording Time Calculator formula works
The formula divides usable storage by the combined bitrate of all streams, then converts the result from seconds to hours:
Recording time (hours) = SD card capacity (GB) × 8,000 × usable storage percentage ÷ 100 ÷ (bitrate per stream (Mbps) × number of streams × 3,600)
The calculator uses decimal storage units, where 1 GB equals 8,000 megabits. Multiplying capacity by the usable percentage gives the storage available for footage. Multiplying the per-stream bitrate by the number of streams gives their combined data rate. Dividing usable megabits by that rate gives seconds, and dividing by 3,600 converts seconds to hours.
Worked example: 128 GB card at 8 Mbps
Assume one security camera stream records continuously at an average of 8 Mbps, including any audio, and 90% of a 128 GB card is available for recordings. These are the calculator’s illustrative default inputs:
- SD card capacity: 128 GB
- Bitrate per stream: 8 Mbps
- Usable storage: 90%
- Streams sharing the card: 1
The usable storage is 128 × 8,000 × 0.90, or 921,600 megabits. At 8 megabits per second, that storage lasts 115,200 seconds. Dividing by 3,600 gives a Recording Time of 32.00 hours.
This does not guarantee that the camera will retain exactly 32 hours of footage. It is an estimate based on the stated average bitrate and usable storage assumption.
Use cases for the SD Card Recording Time Calculator
Choosing an SD card for a security camera: Compare card capacities to see which might provide the continuous recording window you need. A larger card generally holds more footage when the bitrate and other conditions remain the same. Also check the camera manufacturer’s supported card capacities before buying.
Planning local footage retention: If your camera overwrites old footage, the estimate can help you decide how often to review or save important clips. For example, an estimated 32-hour window means an event may be overwritten after roughly that period under the example assumptions.
Comparing camera settings: Higher resolution, frame rate, and image quality settings can affect the recording bitrate. If you know the average bitrate associated with each setting, you can compare their estimated recording times and choose a balance that suits your needs.
Estimating storage for shared streams: Some devices save more than one video stream to the same card. Enter the total number of continuous streams when they share the card and have the same average bitrate. For example, a 64 GB card at 100% usable storage with two 4 Mbps streams has an estimated recording time of 17.78 hours.
Checking an existing setup: Compare the estimate with how much footage your camera actually retains. A large difference may indicate that the average bitrate, usable storage, recording schedule, or number of streams differs from your assumptions.
Other factors to consider when calculating Recording Time
Variable bitrate: Many cameras adjust the amount of data they record as a scene changes. Movement, rain, foliage, low light, and image noise can affect the bitrate. A value from a quiet scene may not represent the average over a full day.
Continuous versus motion-triggered recording: This calculator assumes continuous recording. If your camera records only when motion is detected or follows a schedule, the calendar time covered by the card can be longer. That period depends on how often and how long the camera records.
Audio and additional data: Audio can use storage alongside video. Device-specific metadata, indexes, and file handling can also affect available space. Use a bitrate that includes audio where applicable, and choose a usable storage percentage that allows for overhead.
Unequal stream bitrates: The calculator applies the same bitrate to every stream. If streams sharing a card have different average rates, their combined rate divided by the number of streams can be used as an estimated per-stream average, provided they all record continuously.
Loop recording: When loop recording is enabled, a full card may continue recording by replacing older files. The estimate describes the approximate amount of footage retained before overwriting, not the total time the camera can remain in operation.
Card compatibility and condition: Capacity alone does not determine whether a card is suitable for a camera. Check the device’s supported card type and capacity, and follow its guidance for cards used in continuous recording. Formatting and device behavior can also affect how much space is available.
Frequently asked questions
How long will a 128 GB SD card record security camera footage?
It depends on the average bitrate, usable storage, and number of streams. With the calculator’s illustrative defaults of 8 Mbps, 90% usable storage, and one continuous stream, a 128 GB card provides an estimated 32.00 hours of recording time.
Does a higher bitrate reduce SD card recording time?
Yes. A higher average bitrate writes more data per second, so the card fills sooner when capacity and all other inputs stay the same. For example, doubling the bitrate approximately halves the estimated continuous recording time.
Does adding a second camera stream halve recording time?
It does if both streams share the same card, record continuously, and have the same average bitrate. Together, they use twice the data per second of one stream. If their bitrates or recording schedules differ, actual retention will differ from that simple comparison.
Why is usable storage less than the advertised SD card capacity?
Formatting, system files, and other device overhead can reduce the space available for recordings. The calculator lets you enter a usable percentage to account for these factors. The appropriate percentage depends on the card and camera; 90% is an illustrative assumption.
Will the calculator predict exactly when old footage is overwritten?
No. It estimates continuous footage retention using the values entered. Variable bitrate and the camera’s file handling can change when overwriting occurs. Check your camera’s actual retention over time if you need a more reliable planning figure.