Choose the method your reel supports
Start with the evidence you already have. Give each reel its own inventory ID before measuring so photos and calculations stay matched. The other wire selling guides cover identification and condition separately.
| Evidence available | Method | Main limitation |
|---|---|---|
| Original footage and complete pull records | Original length minus all removed lengths | Missing cuts make the balance too large |
| Sequential marks near both ends | Difference between end marks | Unmarked tips need separate measurement |
| Current gross weight and reliable empty-reel weight | Net cable weight divided by unit weight | Wrong cable specification gives wrong footage |
| Cable diameter and winding dimensions | Reel geometry estimate | Gaps and uneven layers affect the result |
| No reliable records or measurements | Photograph and report footage as unknown | Do not turn a visual guess into a stated quantity |
A partial reel may hold one continuous piece or several separate cuts. Those are different inventories even when the combined footage is equal.
Read sequential markings and subtract recorded pulls
Southwire documents sequential footage markers on SIMpull THHN and SIMpull XHHW-2 in sizes 1/0 through 1000 kcmil. Do not assume every brand or smaller size has them. Check the actual print on your THHN building wire or XHHW-2 feeder wire.
- Photograph a readable length mark near the accessible outside end.
- Find the inside-end mark only if it is safely accessible, or use a recorded mark tied to that reel.
- Confirm both numbers belong to the same continuous piece and use the same units.
- Subtract the smaller number from the larger.
- Measure any cable between each printed mark and its physical end, then add those tip lengths.
Illustrative example: marks of 1,840 FT and 1,215 FT give 625 feet between the marks. The remaining physical length includes any unmarked tips. A lone mark reading 1,840 FT does not mean 1,840 feet remain.
With pull records, subtract all removed lengths, including setup cuts and unused portions removed from the reel. For example, an original 1,000 feet minus recorded cuts totaling 375 feet leaves a documented balance of 625 feet. Label it a record-based balance if it has not been measured.
The reel tag and jacket print guide helps separate length marks from product, date and lot codes.
Estimate footage from current net weight
Southwire's packaging reference lists footage and gross, tare and net weights as reel-tag information. An original gross weight is not the current weight after cuts.
Remaining feet = (current gross weight − current tare weight) ÷ cable weight per foot.
If the product sheet gives pounds per 1,000 feet, use:
Remaining feet = net cable pounds × 1,000 ÷ cable pounds per 1,000 feet.
Tare means the empty reel and any non-cable packaging included in the weighing setup. Do not count an axle, pallet or attached handling equipment as cable. A wet wooden reel can also make an old tare figure unreliable.
Illustrative example: assume a current gross weight of 310 pounds, tare of 60 pounds and complete cable weight of 500 pounds per 1,000 feet. Net cable weight is 250 pounds. The estimate is 250 × 1,000 ÷ 500 = 500 feet. These are example inputs, not specifications for a particular wire size.
Use the exact product's complete weight, including insulation, jacket, shields and armor. A wire weight chart is a starting reference, not a substitute for matching the construction.
Measure the winding, not the flange
For a round cable wound evenly across the reel, collect these measurements in inches. Keep the reel secured and do not reach into an unsupported load.
| Symbol | Measurement | What to avoid |
|---|---|---|
| B | Diameter of the center barrel | Using the center hole diameter |
| D | Outside diameter of the remaining cable winding | Measuring the larger reel flange |
| T | Width occupied by the winding, between flanges | Including flange thickness or unused width |
| d | Overall diameter of the complete cable | Using bare conductor diameter or AWG size |
| H | Radial winding depth, calculated as (D − B) ÷ 2 | Treating the diameter difference as radial depth |
Measure D at several places if the winding looks uneven. Use calipers gently on an accessible cable end or look up overall diameter by exact catalog number. Do not squeeze soft insulation to get a smaller reading.
For 250 to 500 kcmil conductors, kcmil describes conductor area. It is not the outside diameter needed here.
Reel footage calculator formula and worked chart
Quabbin publishes a reel-factor formula for approximate cable capacity. Using the remaining winding depth instead of the available full-reel depth gives this estimate:
Estimated feet = 0.262 × (H + B) × H × T ÷ d².
All four dimensions must be in inches; the result is in feet. Square the cable diameter before dividing. The formula assumes regular winding and does not verify continuous length.
Illustrative example: B = 12 inches, D = 24 inches, T = 16 inches and d = 0.50 inch.
- H = (24 − 12) ÷ 2 = 6 inches.
- Reel factor = 0.262 × (6 + 12) × 6 × 16 = 452.736.
- Cable diameter squared = 0.50 × 0.50 = 0.25.
- Estimated footage = 452.736 ÷ 0.25 = 1,810.944 feet.
Report about 1,810 feet, dimension estimate, not the calculator's decimal result.
This original comparison chart holds barrel diameter, winding width and cable diameter at the example values above. Results are rounded to the nearest ten feet.
| Remaining winding diameter D | Radial depth H | Estimated footage |
|---|---|---|
| 20 inches | 4 inches | 1,070 feet |
| 24 inches | 6 inches | 1,810 feet |
| 28 inches | 8 inches | 2,680 feet |
The chart shows why a reel that looks half full is not necessarily half its original footage. The empty barrel takes up space, and outer wraps are longer than inner wraps.
Know when the formula does not fit
Do not apply the single-round-cable formula to flat cable, twisted assemblies or several independent conductors wound together. Treat segmented and parallel reels separately using their tags and cut records.
Loose winding, crossed wraps, gaps and a partly filled top layer can make a smooth-cylinder estimate too large. Do not apply an arbitrary correction factor. Check against weight or markings instead.
List partial reels and cut lengths by continuous piece, not just combined feet. If methods disagree, recheck units, tare and product diameter before choosing a quantity.
Keep Arizona project reels separated
SRP's October 2024 Eleven Mile Solar System announcement identifies a solar and battery project near Coolidge in Pinal County. For a solar-and-storage closeout, keep project and circuit labels attached. Do not merge every reel into one footage total.
When inventorying a similar Arizona closeout, separate solar PV wire from medium-voltage cable. They need different diameter and weight inputs. Preserve sealed cable ends rather than opening them just to search for a hidden footage mark.
Record enough detail to check the estimate
Before sending an inventory, include:
- Reel ID, Arizona location, manufacturer and catalog number.
- Type, conductor metal, size, color and conductor count.
- Estimated footage per continuous piece and the method used.
- Photos of the whole reel, tag, jacket print and accessible end marks.
- Scale reading and tare evidence, or B, D, T and d measurements.
- Any gaps in pull records, separate cuts or visible damage.
We buy all types of electrical wire and cable, new, unused, leftover or used, including partial reels and cut lengths. Send photos and your documented estimate with an offer request, and we will make an offer. We pick up anywhere in Arizona.