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 (Full Track) or 2 channel
stereo. The Dual Track listing is for recording in both directions (1/2 track mono).
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 records varies from 18 to about 22
© 2012 Corey Bailey
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