There are a LOT of variables when it comes to sizing 1/4-inch Open Reel or Reel-to Reel tapes:
Track Format:
- "One Side" track formats, which record in one direction only:
- Full track mono, recording only one track on the full width of the tape
- Half-track stereo, recording two channels, each on half of the tape width,
- Four-track stereo, recording four channels on four tracks (quadrophonic or multitrack sync recording)
- "Two Side" track formats, recording in both directions, requiring the listner to "flip" the tape to play the other side
- Half-track mono, recording on half the width of the tape, in two directions
- Quarter track stereo, recording two channels on two of the four tracks in each direction
- Four-track mono, recording four discreet tracks with separate program on each track, requiring two flips to hear all four tracks.
On top of that, there are 5 possible speeds (and one wild card) at which the tape can run. The faster the speed, the better the sound quality:
- 30 inches per second - professional mastering
- 15 inches per second - high quality home recording and professional mastering
- 7.5 inches per second - Most common HiFi stereo recordings with excellent sound
- 3 3/4 inches per second - Economy recording with reasonable sound, common on commercial music reels
- 1 7/8 inches per second - "Lo-fi" recordings common in "living letter" voice recordings and transcriptions
- Variable speed - an artifact of cheap battery powered recorders that would slow down as the batteries run out. Yes we can compensate for that.
And then there are three common thicknesses of tape which determine how much tape can go on a reel:
- 1.5 mil - known for sturdiness
- 1 mil - Long playing
- .5 mil - Extended play
Finally, you have the various reel sizes (measured diagonally):
- 10.5-inch reels, mostly used for professional recording
- 7-inch reels, common HiFI variety, available with small hub and large hub
- 5-inch reels, used by portable recorders
- 3-inch reels, used by ultra portable "pocket" recorders
Bottom line, the more tracks, the thinner the tape, the larger the reel and the slower the speed, the more time you can have on a tape.
If the tape is in a branded box, it probably has the specs listed (see picture), If someone wrote the speed and track format on the box, you can find a the length in this chart:
Open Reel Tape Speed Comparison
| Reel Size |
Thickness |
Tape Length |
Recording Time per side at Tape Speed (Minutes)* |
| (Inches) |
(Mil) |
(Feet) |
1 7/8 ips |
3 3/4 ips |
7.5 ips |
15 ips |
| 3 ¼ |
1.5 |
250 |
27 |
13 |
7 |
3 |
| 3 ¼ |
1 |
400 |
43 |
21 |
11 |
5 |
| 3 ¼ |
0.5 |
800 |
85 |
43 |
21 |
11 |
| 5 |
1.5 |
600 |
64 |
32 |
16 |
8 |
| 5 |
1 |
900 |
96 |
48 |
24 |
12 |
| 5 |
0.5 |
1800 |
192 |
96 |
48 |
24 |
| 7 |
1.5 |
1200 |
128 |
64 |
32 |
16 |
| 7 |
1 |
1800 |
192 |
96 |
48 |
24 |
| 7 |
0.5 |
2400 |
256 |
128 |
64 |
32 |
| 10 ½ |
1.5 |
2500 |
267 |
133 |
67 |
33 |
| 10 ½ |
1 |
3600 |
384 |
192 |
96 |
48 |
| 10 ½ |
0.5 |
4800 |
512 |
256 |
128 |
64 |
*Recording time in one direction (one side). Double time if recorded on both sides. For 30ips pro tapes, half the time of 15 ips.
If no writing on the box tells you the speed, the only way we can figure it out is to play it. Once we do we'll adjust the quote.
Complications
It's hard enough trying to figure out how long a tape is in order to price a transfer job. Open reel tapes especially, and to some degree cassettes, can have hidden problems that fall into the "restoration" category. These include:
- Bad splices.
If the tape was spliced, over the years the splices can dry out, and as it plays the splice comes apart. Usually this can be repaired with no loss of program, but if the tape is damaged around the splice, a few seconds of program may be lost. One splice repair is included per open reel tape, but if more breaks are encountered, extra fees may be added.
- Brittle or stretched tape.
Some older acetate tapes may break under tension from our tape machines, or sometimes just by flexing the tape. We can splice those breaks and use special low tension techniques if necessary. Polyester tapes won't break under tension but they stretch. If a section of tape is found to be stretched it will have to be spliced out.
- Dry oxide.
Some very old tapes dry out over time and the oxide that holds the recording actually flakes off during playback. There is little that can be done with those. You will hear dropouts where the program material has been lost.
- Sticky Shed.
This affects "high output" tapes from the late 70s to the early 90s. The glue holding the oxide absorbs water and become sticky. This either gunks up the heads so the audio quality degrades, or it can actually jam up the mechanism and prevent the tape from playing. At worst, sticky shed can peel away the oxide as the tape unspools, destorying the tape. They can be restored by baking. See our article on Tape Baking. Sticky shed can be found with open reel, cassette, and even videocassettes (especially tapes made by Ampex).
- Tape Hiss, Background Noise or Other Issues.
Amateur recordings sometimes have issues from the get-go caused by mistakes the operator made, or problems with the recorder. These include low recording levels, which when amplified have very bad hiss, background sounds that are louder than the voices you want to hear, overdriven recording levels that are distorted, improper head alignment or speed variations. Our restoration tools can correct many issues, but not all. We will inform you of problems we encounter and estimate cost to restore if restoration is possible.
- Multi-track tapes
Does anyone remember Quadrophonic? In the late 60s and early 70s, 4-channel tapes were a thing, with separate tracks for two additional speakers behind the listener - the original "surround sound." Then for semi-pro use they brought out 4-channel multitrack recorders so that garage studios could do multiltrack recordings onto quarter-inch tape. We can play back 4 channel tapes and mix down 4-channel multitrack recordings. (We do not have capability of mixing down half-inch multilchannel tapes.)
How to Order
When it comes to quoting your tape transfer job, we’ll estimate based on the label on the box, and if there's no label we'll just make a guess, but the final bill will reflect actual time on tape, which may be more or less than the estimate.
If you have tapes to send and are unsure, send us a picture and we can probably guess from there what you have. We at Advent Digitizing look forward to making your precious recordings listenable again!
Request your Audio Transfer Quote