What is the cubic ft capacity of this old model

It is the '25' in your model number.

Total Capacity. 25 cu. ft. Refrigerator Capacity. 15 cu. ft. Freezer Capacity 10 cu. ft.

Here is the manual in case you need it.
http://kitchen.manualsonline.com/manuals/mfg/whirlpool/ed25rfxfw01_2.html?p=1

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Total Capacity (Cu. Ft.)
20.5
Refrigerator Capacity (Cu. Ft.)
15.27
Freezer Capacity (Cu. Ft.)
5.26

source
https://www.manualslib.com/manual/54236/Frigidaire-Ffht2117l-W.html?page=2#manual

Total Refrigerator Capacity 26.70 cu ft Measure Freezer Fresh Food Total Capacity Cubic Feet 7.66 cu ft 19.02 cu ft 26.70 cu ft Liters

After some work online...I found this advertisement buried among a bunch of other ads:
Magic Chef RB15-1A: Top-freezer style with 14.6 cubic ft. capacity and optional ice maker -- $439.

So, as I suspected the "15" in the model number is the cubic feet (total I would say). The 14.5 is probably actual, with the unit "rated" as a 15 CF.

Naturally, to find the cu. ft of the freezer, measure in inches then multiply the width X height X depth and divide that resulting rather large number by 1728 to get your cubic feet of the freezer.

You could also do the same with the refrigerated section, and add the results together and they should be near 14.5 total.

This is the information I could find.

Refrigerator Type Side-by-Side Total Capacity Cu. Ft. 21.7 Cu. Ft. Refrigerator Capacity Cu. Ft. 14.40 Cu. Ft. Freezer Capacity Cu. Ft. 7.30 Cu. Ft. Energy Star® Qualified Yes
for more information try this link.
Whirlpool Appliances for the Home Kitchen and Laundry Room

Bob

Hello Mary;
My name is Peter. I am a retired field service refrigeration technician.

Freezer Capacity (Cu Ft): 9.61

Overall Capacity (Cu Ft): 25.12

Depth w/ Handle (in.): 32.625

Depth w/o Handle (in.): 32.375

Height to Top of Case (in.): 68.875

Height to Top of Hinge (in.): 69.125

Depth w/Door Open 90 Degrees (In.): 49.875

Refrigerator Capacity: 15.51

Width w/Door Open 90 Degrees (In.): 41.5

Width w/ Door Closed (In.): 35.5

Depth without Door (in.): 28.875

Get cubic foot size by multiplying height x width x depth.
Divide that by 1728. If oven is 12 x 12 x 12 then it's exactly 1 cubic ft.
If 6 x 6 x 6 then it's 1/2 cubic ft or. 50 cu ft

The capacity depends on the exact model number. The TBX18TABWW and similar models are 17.6 cu. ft. The refrigerator holds 13.6 cu. ft. and the freezer 4 cu. ft. This model is 64.25" tall, including the hinge, 28" wide, and 31.25" deep.

The GE S series, including TBX18SIBRWW, are 18.2 cubic feet; the specs are 13.04 cu. ft. for the fridge and 5.13 for the freezer. Total height (including the hinge is) 64.75", 29.375" wide and 31.5" deep including the handle. (It takes up 58" with the door open.)

The J series has the same total capacity and dimensions as the S series.

Remember to leave 0.75" free on both sides and 1" at the back and top for air to circulate around the refrigerator.

You can find your exact models specs and manuals here: http://www.geappliances.com/service_and_support/literature/ . Enter the model number in the search box and click submit. Dimensions are provided in the Quick Specs for most refrigerators. The model number will be on a plaque in any of the following spots:
1) On the ceiling of the freezer near the front
2) By the temperature control
3) On the inside wall of the refrigerator near the crisper drawer on either side
4) Behind the crisper drawer
5) On the bottom front of the refrigerator

I hope this helps.

Cindy Wells

This is called a 21 Cubic Ft unit.

The actual specifications are:

Freezer Capacity: 6.5 Cu. Ft.

Refrigerator Capacity: 14.5 Cu. Ft.

Total Capacity: 20.9 Cu. Ft.