AI audio duration estimator
Before you spend AI voice credits, it helps to know roughly how long your audio will run and what it will cost. This estimator turns a word count into an estimated duration for different content types and speaking rates, then approximates the character-based credit cost charged by common AI voice tools.
How it works
Spoken duration is driven by speaking rate, measured in words per minute (WPM). A relaxed audiobook read averages around 135 WPM, conversational narration about 150, and a punchy ad read 170 or more. The tool divides your word count by the selected WPM to get minutes, then formats minutes and seconds. For cost, it estimates characters (English averages roughly 5.8 characters per word including spaces) and multiplies by a per-character rate that approximates each platform’s billing tier, so you get a budget figure in credits.
Notes and examples
- A 500-word podcast segment at 150 WPM runs about 3 minutes 20 seconds.
- The same 500 words as an audiobook at 135 WPM stretches to about 3 minutes 42 seconds — slower pace, longer file.
- IVR and phone prompts should be estimated at a slow rate; callers need time to process menu options, so the extra seconds are intentional.
- Treat the credit figure as a planning estimate. Pauses, SSML breaks, and re-generations all add to real usage.
Speaking rate quick reference
| Content type | Typical WPM | Why |
|---|---|---|
| Audiobook narration | 130–145 | Listeners follow a sustained read; slower aids comprehension |
| Conversational / podcast | 145–160 | Natural dialogue pace; most AI narration voices default here |
| Explainer / tutorial | 140–155 | Slightly measured to let concepts land |
| Advertisement / promo | 160–180 | Energy and urgency; broadcast ads are often edited to feel faster |
| IVR / phone menu | 110–130 | Callers need time to hear options and reach for a key |
| Audiobook children’s | 110–130 | Young listeners benefit from deliberate, clear delivery |
Credit cost: what the estimate represents
AI voice platforms bill per character generated, not per second of audio. The character count for your script can be estimated from word count, then multiplied by a per-character rate. A 1,000-word script at roughly 5.8 characters per word generates around 5,800 characters.
Because different voices, models, and tiers on the same platform carry different per-character rates, the tool uses a representative figure that approximates common pricing at standard tiers. Treat the number as a planning ceiling rather than an invoice — actual spend depends on your specific plan, the voice selected, and any regenerated takes. Always check your provider’s current pricing page before committing to a production run.
Common planning mistakes
Forgetting SSML pauses. Speechmarks and SSML break tags add silence without adding words. A script with many pauses runs longer than the WPM formula suggests.
Underestimating re-generations. Getting the right emotional tone often takes two or three attempts on each section. Budget 1.5× to 2× the character count for a polished finished piece.
Mixing voice styles in one estimate. If your project has a slow narrator section followed by a faster dialogue exchange, run them separately and add the results rather than applying one average rate to the whole word count.