Audio Duration & File Size Calculator
This audio duration calculator works as a file size calculator, a bitrate calculator, and a storage planner in one — convert between duration, file size, and bitrate for any compressed format (MP3/AAC/Opus) or uncompressed PCM/WAV settings. Use the podcast size estimator tab to plan episode storage before you record. It’s a calculator; no files are uploaded or processed.
ℹ Estimates assume a constant bitrate. Real MP3/AAC files are often VBR (variable), and tags/containers add a little overhead, so actual sizes vary by a few percent. Lossless (FLAC/ALAC) has no fixed bitrate — it depends on the audio. Sizes use decimal units (1 MB = 1,000,000 bytes); Windows shows binary (1024-based), so its “MB” look a bit smaller.
1 · Audio format
How long is a file of a given size?
How big is a file of a given length?
How many hours fit in my storage?
Common formats — size per hour
Approximate sizes for one hour of stereo audio at typical settings (decimal MB/GB).
How the Math Works
Audio file size and duration are tied together by the bitrate — the number of bits used per second of audio. The core relationship is file size (bytes) = bitrate (bits/s) × duration (s) ÷ 8, and rearranged, duration = size × 8 ÷ bitrate. For compressed formats (MP3, AAC, Opus) the bitrate you choose already includes both channels, so a 128 kbps stereo file and a 128 kbps mono file are the same size. For uncompressed PCM/WAV, the bitrate is computed from the recording settings: sample rate × bit depth × channels — e.g. CD quality is 44,100 × 16 × 2 = 1,411,200 bits/s (1,411 kbps).
These are estimates because most compressed encoders use variable bitrate (VBR), spending more bits on complex passages, so the size is an average. Containers and metadata (ID3 tags, MP4 atoms, the 44-byte WAV header) add a small fixed overhead — negligible for long files, noticeable for very short ones. Lossless formats like FLAC compress by content (often 40–60% of WAV), so they don’t have a fixed bitrate to calculate from.
For podcast producers and voice-over artists, the math scales simply: a 60-minute episode at 128 kbps MP3 is about 57.6 MB, while dropping to 64 kbps (common for speech-only mono podcasts) halves that to roughly 28.8 MB without a noticeable quality loss for voice. Stereo doubles the raw PCM data but has no effect on the size of a compressed file whose bitrate already accounts for both channels — a common source of confusion. If you want to hear exactly what a chosen bitrate sounds like before committing to it, pair this calculator with the audio spectrum analyzer to check whether high-frequency content survives the codec.