How much storage do call recordings need?

A recorded call is a stream of samples, so its size is arithmetic: length in seconds, times bitrate in bits per second, divided by eight, plus a small file header. A four-minute call stored as an ordinary 8 kHz 16-bit WAV is 3.84 megabytes. That part takes ten seconds to work out and nobody gets it wrong.

What people get wrong is everything around it. Which format the file is actually stored in, whether both sides of the conversation are kept separately, how many copies exist, and above all how long the whole pile is kept before anything is deleted. That last one moves the answer more than the codec does, and it is not close.

The stored bitrate is the only property of the audio that matters. Everything else is multiplication.

Those last two rows are a trap, and it is worth naming. The format a recording is stored in is often not the codec the call travelled on. A call carried over G.729 at 8 kbit/s is routinely written to disk as uncompressed 16-bit PCM, at which point it occupies sixteen times what the wire figure suggests. If you are sizing a disk, the number you need is the bitrate of the file that lands on it, which you can get by dividing a real recording's size by its length.

While we are in Cisco's bandwidth table, one more thing that page is often misread for: it adds 40 bytes of IP, UDP and RTP header to every packet. That is network overhead. It never reaches a disk, and it has no business in a storage calculation.

Recording each side of the conversation on its own channel is worth having. It is what lets you hear who talked over whom, and it is what makes a recording usable for anything more than confirming an address.

It is also, precisely, double the file. A second channel is a second stream of samples written into the same container. The call is not one second longer for it.

That matters more than it sounds, because it lands differently on different bills. On a provider that charges for a recorded minute held, dual-channel recording costs nothing extra at all: a minute is a minute. On a provider that charges per gigabyte, it costs exactly twice as much. Same decision, same recording, two completely different answers depending on what your supplier counts.

Here is the part that surprises people in the cheaper direction.

If your retention window is actually enforced, the oldest recording is deleted as a new one arrives. So storage climbs while the window fills, and then it holds flat forever. The plateau is the number to buy against, not the accumulating total.

Take a small business recording 120 calls of four minutes on each of 21 working days a month, as an ordinary 128 kbit/s WAV, one channel:

120 calls x 240 s x 16,000 bytes/s = 460.8 MB a recording day 460.8 MB x 21 days = 9.68 GB a month

Multiply that month by twelve and you get 116 GB, which is the number most people write down. With a 90-day retention window the true figure is 29 GB, and it stops there. With a 30-day window it is 9.7 GB. Only if you keep everything for more than a year does the naive extrapolation become right.

Two multipliers sit on top of the plateau and are easy to forget. Copies: a backup is charged like the original on any per-gigabyte rate, so two copies is two times the bill. Margin: whatever you add over the estimate, because a real month is never the average month.

This is the other place a recording budget goes wrong, and it is a reading error rather than an arithmetic one.

Making a recording is often charged once, per recorded minute. Keeping it is charged again, per month, for as long as you keep it, and depending on the supplier that second charge is levied either per recorded minute held or per gigabyte held. They are different quantities. A per-minute-per-month rate does not care what format you chose or how many channels you kept; a per-gigabyte rate cares about nothing else.

They are also not each other's competitors. Raw object storage holds bytes you put there. A voice platform's recording feature creates the recording, keeps it, serves it back and bills the minute for doing all of that. Putting the two rates side by side and picking the smaller number compares a bucket with a service, and the comparison tells you nothing. Read the line that matches your own bill, price the decision you are actually making, and leave the other line alone.

How long to keep recordings is the input that moves the answer most, and it is the one input no calculator can supply.

Retention periods come from privacy law, from sector rules, from the contracts you have signed and sometimes from a specific request by a specific customer. They differ by country, by industry and over time. Health, financial and public-sector rules in various jurisdictions all point in different directions, and several of the ones people quote with the most confidence do not actually prescribe a period for call recordings at all. Anyone offering you a preset labelled with the name of a statute is guessing on your behalf.

What the arithmetic can tell you is the consequence, and it is clean: storage is linear in retention. Double the window, double the disk, double the monthly line on either billing basis. If a retention decision is being argued on cost, that is the number the argument needs. What you have to tell a caller before the recording starts, and who may listen afterwards, is a separate question covered in what the law asks before you record a call.

The call recording storage calculator does all of the above in your browser. Put in your call volume, the format, the channel count, your retention window and your own storage rate, and it returns the size at the plateau, the fill curve to get there, what a different window would cost, and the two billing bases kept apart. Every bitrate and price on the page is cited to the page it came from with the date it was read, and your own rate is the input, so the answer stays true when a vendor moves a price.

Nothing you type is sent anywhere and no recording is read: there is no upload on that page and no endpoint behind it.

Once you have the number, the settings that decide how much of it you fill are the ones on the phone system itself: whether recording is on for everyone or is the choice of the person answering the call, whether both sides are kept separately, and what happens when a window expires. And if you are pricing the whole thing rather than just the disk, what a seat costs is the other half of that sum.