The charts on this page are provided to give you an idea of running times for
various reel-to-reel audio tapes and records. Starting with analog tape, the chart
below from the box of an old reel of Irish brand tape, is calculated for 7” reels.
The lengths shown on the left of the chart represent the different thicknesses of
The Single Track listing is for recording in one direction. This column can be
used for full track mono or any format stereo recording, recorded in one direction.
The Dual Track listing is for recording in both directions. 1/2 track mono was the
available consumer format when this tape was produced. The same “Dual Track”
column can be used to calculate 1/4 track stereo recorded in both directions.
This tape is from the late 1950’s. Notice the price stamped just below the brand
logo. It’s barley readable, but it is $2.88. Pretty pricey for 1958.
1200’ is 1.5 mil thickness (1 mil = one thousandth of an inch)
1800’ is 1 mil thickness.
2400’ is 0.5 mil thickness.
My deepest sympathies if you have any audio tape that is 0.5 mil (1/2 mil). It was
fragile in its day, and it is incredibly fragile now. The tape in this particular box is
1.5 mil acetate, and it played just fine. There is a picture of the reel
if you are
The running times listed above represent the absolute maximum time available.
The average running time for a 10” Dia. 78 RPM record is about 3 minutes. The
average running time for 12” Dia. 33-1/3 RPM micro-groove records varies from
18 to about 22 minutes.
© Corey Bailey Audio Engineering
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