Reel Measurement Tutorial

How to Measure your Reel for Excellent Results

GPS works with known guide heights and known upsweep angles for the reel you have chosen. With this information and a few proprietary formulas, GPS can tell you the best place for your selected guides. An error in measurement results in an erroneous angle which can make a difference in the placement of your guides. This variable is the reason we suggest working the guides into a final position by actually casting taped guides before doing your final wrap. The old computer adage; “garbage in garbage out” holds true with GPS. If you transpose numbers or enter them in the wrong box GPS cannot successfully calculate position. If you’re measurements are inaccurate your resulting layout will not perform as well as it could. A little care in measuring your reel will result in a rod that meets true “high performance” standards. We refer to GPS as a “starting point” to better guide placement. With that in mind it’s a good idea to give yourself a “cushion” to cover small errors in measurement. We generally suggest that any guide can move and inch in any direction while searching for a final layout. This flexibility allows you to find the “perfect” set-up before a final wrap.

Material You Will Need

To prepare, we prefer a piece of poster board rather than typing paper since the added thickness helps keep the project flat and easier to measure. We suggest taping the edges of the board down to the table. You will need a pencil or pen, a ruler and a 90˚ triangle or square. It is also helpful to have a caliper to make final measurements in millimeters for GPS. We also suggest clay or some kind of putty to hold the reel in position while measurements are being made. We prefer a product normally used to hold posters on the wall. You can find it in the picture hanging area of your local pharmacy with names like “Tacky Putty” or “Blue Goo” (by the way, we find many uses for this stuff including holding micro guides while they are hot glued on a blank or melting glue in a micro top without burning your fingers).

Step 1

Remove the spool from the reel. Draw a straight line all the way across your board at the bottom to represent the rod blank. Use the putty to secure the foot of the reel EXACTLY on the line representing the blank (yes, we realize the reel is upside down, but we are only looking for measurements and somehow this seems easier to eyeball).

Reel Measurement Diagram 1

Step 2

With the reel foot secure and straight on the rod blank line, use a wide ruler and pinch it gently up against the spool axle. This is the most important step in the process so take your time. Check the ruler and try to make it perpendicular (90˚) to the surface of the paper. When you are satisfied that the ruler is touching the spool axle all along its edge and the ruler is 90˚ to the paper, scribe a line along the bottom edge of the ruler. Congratulations, you have just captured the angle of the spool relative to the blank!

Step 3

Mark the back edge of the reel. You can actually just eyeball this measurement since drop will always have an identical relationship to distance for any projected angle.

Reel Measurement Diagram 3

Step 4

Mark the tip of the spool axle on the spool axle line you drew in step 2. You can actually just eyeball this measurement since drop will always have an identical relationship to distance for any projected angle.

Reel Measurement Diagram 4

Step 5

Position the ruler precisely on the spool angle line drawn in step 2 and project the line past the rear reel mark and the spool tip mark as shown below.

Reel Measurement Diagram 5

Step 6

At the point where the projected spool axle line intersects with the “rear of reel” mark, use a square or 90˚ triangle to draw a line (A) perpendicular to the rod blank line. Do the same (B) for the spool tip mark.

Using calipers, measure the length of Lines A, B, & C. A & B are measured from the intersecting point on the spool axle line to the top edge of the rod blank line.

Note these numbers in millimeters and enter them in the boxes in the GPS interface. Label the measurements with the name of the reel and establish a reference file for the future. Choke point and reel upsweep are ALWAYS the same for a particular reel.

Reel Measurement Diagram 6

The information generated from this input will determine the upsweep of your reel. If you do not know what reel will be used, locate a similar reel series such as a 2500, 3000, 4000 and measure it. There may be some variation, but most reels in a given series will be within a degree or so of one another. One degree can sometimes move guides up to four inches so if you don’t have the reel to be used you need to be prepared to move guides a greater distance than if you were measuring the exact reel you plan to use.

Another method is to use the 27X formula created by Tom Kirkman. This method attempts to achieve the same height and angle information as an estimate based on a multiplier of the spool diameter. It is a good alternative, but not as accurate as actual measurements. Again, be prepared to move guides more than those positions generated by actual reel measurements.

NOTE: The majority of reels (not including the largest surf reels and some offshore reels) will have an upsweep that falls in a range of 2 to 4.5 degrees. This is represented by a variation of approximately 10 mm in the A & B lines. If your measurements show that “A” is 20 mm higher than “B”, you have most likely made an error in measurement. In most cases, A & B will be within 6 to 13 mm of one another with 10 mm being  “average”.


Anglers Resource is building a library of information that will make locating guides for ANY reel much faster and more reliable. The “Reel Model” tab at the GPS calculation site will list reels that have been successfully measured by builders and supplied to us. If you measure a reel and the resulting placement provides exceptional performance, PLEASE mail that information so we may include it in the library of  reels. Include Brand and model number of reel and your measurements A, B & C in mm or inches.

NOTE: The accuracy of your measurements will be apparent in the performance of the rod/reel. Please do not forward measurements from set-ups that perform at “average” levels. If your measurements were “spot on” and the performance of your layout is exceptional, by all means PLEASE share it with other builders.