I spooled some popular reels to see the actual line capacity. First was the Rob Allen reel. Here's the stated capacity
QuoteThe Rob Allen reel is Constructed from 30% glass filled Nylon with graphite filled acetyl bushes and a stainless steel thread on the drag nut. --- The dead end attachment to the spool ensures that this reel is able to stand up to even the harshest pressure exerted by world record fish. --- The stainless wear surface around the line lead ensures that line is able to run smoothly and will never wear into the reels line guide. --- With the entire reel only weighing 95g and able to hold 55meters of 2mm line, this reel is extremely light for it's capacity. -- Cut-outs assist with drying of the line whilst the reel is easily fitted to most Euro Style guns and a dovetail bracket ensures easy removal
In fact the Rob Allen reel took 150ft (45m) of Speardiver 1.9mm X-Line. Now I could have spooled it very carefully laying down the line tightly against itself in perfect layers to increase capacity. But that's not something you can do in real world conditions. Besides you want to lay down the line in a criss-cross pattern every few layers to prevent the line burying into itself when paying out. I could have also filled the reel right to edge of the spool. But again that's not something you want to deal with in the water. You can see in the pictures the line is 3/16" (5mm) from the edge. In any case 45m is sufficient line for most situations.
This is how I measure line. In Cuba Braza is a unit of measurement used by fishermen and spearfishermen. The word braza is similar to the Spanish word brazo which means arm. According to the conversion website I linked to, one braza is approximately 5.5ft. To measure brazas hold the line firmly with the left hand and loosely with the right, extend the arms all the way sideways letting the line slide through the right hand and stretch across your chest. When the arms are fully extended pinch the line with the right hand and pass it to the left repeating the process. It's quite accurate if you hold the line with the fingertips.
It's a convenient and fast way to measure line when out on the water. When Cuban guys state depth in brazas I take it as an approximation because it really depends on the arm length of the individual doing the measuring. It just so happens the distance between my outstretched hands is 6ft. The Rob Allen reel as you see it in the pictures took exactly 25 Dan brazas 
