Original duration (seconds)

Playback speed (×)

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Playback speed vs duration chart: how 0.75x to 2x speed changes audio runtime — How playback speed changes duration: 60 minutes at 0.75x to 2x

Method & verification

How This Tool Works

Calculation Method

Reads Original duration and Playback speed, then returns the result shown on this page.

Site methodology

BoringToolsKit methodology and verification standard

No unrelated authority link is added merely to make this page look sourced. Tool-specific external sources are shown only when they directly support the method, rate, or rule.

Assumptions to Verify

Inputs are treated exactly as entered.
Verify important decisions with current authoritative information.

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Worked example: the arithmetic behind a 1.25x speedup

Take a 180-second podcast segment played at 1.25x. The new duration is original divided by speed: 180 / 1.25 = 144 seconds, a saving of 36 seconds. The percentage change confirms it: (1/1.25 - 1) x 100 = -20%, so playback runs 20% shorter.

Now reverse it. A 120-second clip slowed to 0.75x lasts 120 / 0.75 = 160 seconds, and (1/0.75 - 1) x 100 = +33.3% longer. Notice the asymmetry: slowing to 0.75x stretches time more than speeding to 1.25x shrinks it, because the divisor sits below 1. A 2x speedup halves duration exactly (100 / 2 = 50 s), while 0.5x doubles it, yet neither is a mirror of the other in percent terms unless the products multiply to 1.

Limits worth knowing before you trust the number

The formula assumes constant playback rate, which real tools break. Audio editors with 'preserve pitch' use time-domain stretching (WSOLA or phase vocoder) that inserts or removes tiny grains; above roughly 1.5x or below 0.5x, artifacts grow and effective intelligibility drops. A 3x speedup gives 300 / 3 = 100 seconds on paper, but speech comprehension studies typically collapse past 2x without training.

Variable-speed automation (ramps from 1.0x to 1.5x over the clip) also invalidates the simple division: average speed is not the arithmetic mean. A 240-second file ramping linearly from 1.0x to 2.0x averages 1.5x by harmonic weighting, giving about 160 seconds, not the 180 you would get from using the midpoint naively in a wrong formula. Use the single-rate calculation only for fixed-speed playback, and treat sub-0.25x or super-3x outputs as rough estimates rather than edit plans.