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Podcast File Size Calculator

Estimate how large your podcast episode will be from its bitrate and length.

How it is calculated

The estimate is MB = bitrate × duration × 60 ÷ 8 ÷ 1000. Here bitrate is in kilobits per second (kbps) and duration is in minutes. Multiplying by 60 converts minutes to seconds, dividing by 8 converts bits to bytes, and dividing by 1000 turns kilobytes into megabytes. Megabytes use the decimal convention (1 MB = 1,000 kB), as hosting platforms do, not 1,024. The gigabytes figure is MB ÷ 1000 and is rounded to two decimals, so short episodes show 0.04 GB or similar. Both inputs must be above zero. The formula fits constant-bitrate audio only; variable bitrate files and tags or cover art make the real file differ somewhat.

Worked example

An episode is 45 minutes long and encoded at 128 kbps. Duration in seconds: 45 × 60 = 2,700. Total kilobits: 128 × 2,700 = 345,600. Divide by 8 to get kilobytes: 43,200. Divide by 1000: 43.2 MB, which is about 0.04 GB. At 192 kbps the same episode would be 64.8 MB, one and a half times as large.

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Common mistakes

  • Entering the duration in seconds or hours. The field is in minutes, so a 1-hour episode is 60.
  • Mixing up kilobits and kilobytes. A 128 kbps rate is 16 kilobytes per second, not 128.
  • Entering a bitrate in Mbps. The field expects kbps, so 0.128 Mbps must be typed as 128.
  • Comparing the result with a size shown in MiB by an operating system, which divides by 1,024 and looks a few percent smaller.
  • Applying the number to a video episode or variable-bitrate file. This formula covers audio at a fixed bitrate only.

About this calculator

This calculator converts a bitrate and duration into a file size using size (MB) = bitrate (kbps) × duration (seconds) / 8 / 1000, dividing by 8 to turn bits into bytes and by 1000 to turn kilobytes into megabytes — the same math that applies to any constant-bitrate audio encoding, whether MP3, AAC or Opus.

Podcast producers use it to predict how large a finished episode will be before exporting, so they can choose a bitrate — commonly 128 or 192 kbps for spoken-word content — that balances audio quality against hosting storage limits and listener download size on mobile data. Audio editors also use it in reverse, working out what bitrate keeps a long-form episode under a hosting platform's file size cap.

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Comments (1)

  • Editorial team

    If your host sets a size limit, solve for the bitrate instead: bitrate = cap in MB × 8,000 ÷ (minutes × 60). A 100 MB cap on a 90-minute episode allows about 148 kbps, and entering 148 and 90 returns 99.9 MB, just under the cap. Tags and cover art add a little, so leave a margin. Does your host impose a cap? Tell us what bitrate you settled on for speech.

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