Examples (as of Feb. 8, 2009):
Package:

Carrier	3 lbs		10 lbs		70 lbs
	2-day air	5-7-day ground	2-day air	5-7-day ground	2-day air	5-7-day ground	2-day air
USPS *	$12	$8	$30	$16	$108	$51
FedEx	$34	$14	$54	$18	$260	$66
UPS	$31	$15	$57	$20	$261	$73

Average 7# per cu ft
Box sizes (home Depot) - 

	

		
Box sizes (home Depot)
 
Fedex Rates
 
UPS Rates
	
	

		
Size
 
LxWxH
 
cu ft
 
lbs
 
dimensional
weight *
 
Cost
 
Cost
 
$/cf
	
	

		
Small
 
16x16x12
 
1.8
	
	

		
Medium
 
18x18x16
 
3
 
20
 
 
$78
$71
 
24
	

		
Large
 
22x21x22
 
6
 
40
 
 
$107
$110
 
18
	
	

		
Extra Large
 
24x24x36
 
12
 
80
 
22
 
$259
 
18
	
		

		
Xerox paper
boxes
 
18x12x11
 
1.4
 

	

* Dimensional Weight (Volumetric Weight)

When you go online to get rates it says they are using dimensional weight to comute it, but don't explain it very well.

I shipped 17 boxes which took up a space about 4' x 6' x 3' in my trailer from New Jersey to California.
The heaviest was around 60 lbs.

It cost $1090.  They estimated it would cost $700 by freight.


Estimates for 18x18x17" 40 lb box  11/29/16
USPS 2-3 days  $107 |  ground 1 - 1 1/2 week $95
Fedex   2 day  $246 |  5 day ground  $48
UPS     3 day  $190 |  8 day ground  $95 3 day select $158

Airline checked baggage
  2nd $35, 3rd $150 max L+H+W = 62"
  
* The U.S. Postal Service (USPS) offers several Priority Mail (2-day) boxes and
envelopes at fixed prices: $4.95 (8-5/8 x 5-3/8 x 1-5/8"), $10.35 for a medium box
and $13.95 (12x12x6") regardless of their weight or destination in the country. 

FedEx and UPS include tracking in prices and automatically cover packages for
up to $100 of declared value.
Tracking and insurance at the post office cost extra. 

Ground service is 5 days with FedEx and UPS
The US Postal Service has a limit of 70 lbs

As of Feb. 2010 a 2nd checked bag on United Airlines is $35

Sample weights with packing:
Electric coffee pot: 3.2 lbs
laptop computer: 8 lbs
Skis: 15-21 lbs
Skis xc: 7-8 lbs 6.25' (190 cm) long 5 days ground $25 UPS, $23 FedEx
Golf bag and clubs: 40 lbs

Pallet or skid size  
48" x 48" is the standard according to ShipNorthAmerica.com
FedEx prefers Grocery Manufacturers Association (GMA).standard 40" by 48" 
 FedEx Express® and FedEx Home Delivery® limits height to 70"
 How to Prepare Shipping Pallets for Freight Shipment | UPS
 A 48x40 pallet 70" high is 77 cf (540 lbs)
 
FedEx freight boxes - Need a business account (must be a business)
48”x 40”x 38”  4-500 lbs 
48”x 40”x 28” 
FedEx Freight Box
FedEx Freight Box Info (pdf)

The lowest price is not always the best value. Sometimes, paying more up front can avoid additional costs later on. By using a freight broker, you might pay a higher initial cost, but often times they are an excellent investment further down the line of your shipment, or if/when something goes wrong.

Freight Class Explained - A Guide to Understanding LTL Freight Class | FreightPros