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Audio Bitrate Calculator — File Size from kbps
Estimate audio file size from bitrate and duration for MP3, AAC, OGG, FLAC and WAV. Plan podcast uploads, size a music library, or work backwards: enter a size limit and find the kbps that fits. 100% client-side — no uploads, no waiting.
How big will my audio file be?
Enter a bitrate and a duration. File size (bytes) = kbps × 1,000 × seconds ÷ 8.
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| Format | Effective bitrate | Estimated size |
|---|
What bitrate fits my size limit?
Enter a target file size and the duration — the calculator finds the maximum bitrate that fits and the best standard preset.
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Playlist / album batch calculator
One track per line: duration bitrate — e.g. 3:45 320 or 1:02:10 128. Durations accept mm:ss, h:mm:ss or plain seconds.
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| # | Duration | Bitrate | Size |
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Audio bitrate recommendation chart
Pick a bitrate by use case. Per-minute sizes computed with the formula above (decimal MB).
| Use case | Format | Bitrate | Size per minute |
|---|---|---|---|
| Audiobook / spoken word | MP3 or AAC mono | 48–64 kbps | 0.36–0.48 MB |
| Podcast / voice | MP3 or AAC mono | 64–96 kbps | 0.48–0.72 MB |
| Music streaming (standard) | MP3 / AAC / OGG | 128–192 kbps | 0.96–1.44 MB |
| High-quality music library | MP3 / AAC | 256–320 kbps | 1.92–2.40 MB |
| Archive (lossless) | FLAC | ≈776 kbps effective | ≈5.82 MB |
| Studio master | WAV | 1,411.2 kbps | 10.58 MB |
Handy rule of thumb: 128 kbps ≈ 1 MB per minute. Halve the bitrate, halve the file — a 320 kbps file is exactly 2.5× a 128 kbps file of the same length.
Worked examples
Every number below is recomputed by the calculator engine on page load — they always match.
3:30 song at 128 kbps (MP3)
128 × 1,000 × 210 ÷ 8 = 3,360,000 bytes
3.36 MB
✓ engine-verified
3:00 song at 320 kbps (MP3)
320 × 1,000 × 180 ÷ 8 = 7,200,000 bytes
7.20 MB
✓ engine-verified
60:00 podcast at 64 kbps mono
64 × 1,000 × 3,600 ÷ 8 = 28,800,000 bytes
28.80 MB
✓ engine-verified
74:00 CD at 1,411.2 kbps (WAV)
1,411.2 × 1,000 × 4,440 ÷ 8 = 783,216,000 bytes
783.216 MB ≈ 0.78 GB
✓ engine-verified
45:00 mix at 192 kbps
192 × 1,000 × 2,700 ÷ 8 = 64,800,000 bytes
64.80 MB
✓ engine-verified
Inverse: 100 MB budget ÷ 60:00
max kbps = 100 × 1,000,000 × 8 ÷ 3,600 ÷ 1,000 = 222.22
222.22 kbps → use 192 kbps (86.40 MB)
✓ engine-verified
Audio bitrate FAQ
What is the formula for calculating audio file size from bitrate?
File size (bytes) = bitrate (kbps) × 1,000 × duration (seconds) ÷ 8. The × 1,000 converts kilobits to bits and ÷ 8 converts bits to bytes. For megabytes as shown by most operating systems: MB = kbps × seconds ÷ 8,000. Example: a 3-minute song at 128 kbps is 128 × 180 ÷ 8,000 = 2.88 MB.
How big is a 3-minute MP3 at 320 kbps?
7.20 MB. Calculation: 320 × 1,000 × 180 seconds ÷ 8 = 7,200,000 bytes = 7.20 MB. That is exactly 2.5× the size of the same song at 128 kbps (2.88 MB), because file size scales linearly with bitrate.
What is the difference between CBR and VBR for file size?
CBR (constant bitrate) keeps the bitrate fixed, so file size is exact: kbps × duration ÷ 8. VBR (variable bitrate) spends more bits on complex passages and fewer on silence, so the final size varies with the audio content — typically about 80–90% of a same-quality CBR encode. This calculator's VBR row uses an 85% estimate and labels it as an estimate.
What is the difference between kbps and kBps?
kbps = kilobits per second, kBps = kilobytes per second — a factor of 8 apart (1 byte = 8 bits). Audio bitrates are almost always quoted in kbps. If your connection runs at 1 MB/s (8,000 kbps), a 320 kbps stream uses just 4% of it.
What bitrate should I use for a podcast or voice recording?
64–96 kbps in mono MP3 or AAC is the standard for spoken word: a 60-minute episode is about 28.80 MB at 64 kbps or 43.20 MB at 96 kbps. Mono halves the bits needed versus stereo with no quality loss for voice. Most podcast hosts accept files up to 200–250 MB, so even a 3-hour episode fits easily at 96 kbps.
Is 320 kbps MP3 better than 128 kbps?
For music, yes: 128 kbps MP3 can show audible compression artifacts on good headphones, while 320 kbps is transparent to most listeners. The trade-off is size — 2.5× larger per minute (2.40 MB vs 0.96 MB per minute). For casual background listening 128 kbps is fine; for a music library you keep forever, 256–320 kbps or lossless is the safer choice.
AAC vs MP3 at the same bitrate — which is smaller or better?
File size is identical at the same bitrate and duration — size depends only on bitrate, not the codec. Quality differs: AAC (used by Apple Music and YouTube) is a newer codec and sounds roughly as good as MP3 at 70–80% of the bitrate, so 96 kbps AAC ≈ 128 kbps MP3. Choose the codec by compatibility, not by size.
Why is WAV so much bigger than MP3 or FLAC?
WAV stores uncompressed PCM audio: 44,100 Hz × 16 bits × 2 channels = 1,411,200 bits/sec (1,411.2 kbps) — about 11× the bitrate of a 128 kbps MP3 and 10.58 MB per minute. FLAC compresses the same PCM data losslessly to roughly 45–60% of the WAV size (about 776 kbps typical, 5.82 MB/min) with zero quality loss.
Related audio calculators
Need sizes from sample rate, bit depth and channels instead of kbps? Try our audio file size calculator (WAV preset–based). For video, size scales the same way — bitrate × duration ÷ 8.
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Free tool by NRTechStudio