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 audio tape, the
chart below is from the box of an old reel of Irish (brand) tape and is calculated
for 7” reels. The lengths shown on the left of the chart represent the different
thicknesses of audio tape.
The Single Track listing is for recording in one direction. This column can be used
for full track mono or any format for 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.
The tape in this particular box is 1.5 mil acetate, and it played just fine.
There is a picture of the reel
(Fig. 1) if you are interested.
The chart lengths
1200’ is 1.5 mil thickness (1 mil = one thousandth of an inch)
1800’ is 1 mil thickness.
2400’ is 0.5 mil thickness.
If you have any audio tape that is 0.5 mil (1/2 mil); It was fragile and hard to work
with in its day, and it is very fragile now. Some 0.5 mil tapes were 3600’ long.
The running times listed above represent the approximate maximum time
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 about 18 minutes to about 22 minutes (I’ve seen as much as 27 minutes).
© Corey Bailey Audio Engineering
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