You may use a metric ruler to measure the size of the pizza on your screen, or you may check the image size (in pixels) by viewing the image online.
To do this, follow these steps (and see the example below):
 

Rightclick (use the righthand or secondary mouse button) on the image and select "View Image" from the menu that will appear  practice on the image at the right:

To View an Image:

Total cost  equals  Base price  plus  Number of toppings  times  Price per topping: 
T  =  B  +  N  *  (P) 
$3.20  =  $2.00  +  3  *  (0.40) 
We can use the pixel width as the approximate diameter of the pizza. So, look at the picture of the pizza and find its width.

 
Then,
since the radius of a circle equals onehalf the diameter, we can divide the the pixel width by two to get a rough estimate of the radius.

 
Next, we "square" the radius (multiply it times itself).

 
Now multiply the radius squared times pi (in this case we'll multiply times three  this is a bit less than the actual value of pi, but the width of the image was greater than the diameter so this will be
balance out somewhat).


Area  equals  pi  times  the radius  ^{squared}

A  =  p  *  r^{2}  
A  =  p  *  50^{2}  
A  =  p  *  2500 
A  =  p  *  2500

A  =  3  *  2500

A  =  7500 
If a 10" Cheese Pizza costs $5.55 and toppings are $.75 each, how much would a 10" pizza with red peppers, bacon and green olives cost?  
If a 14" plain cheeze pizza costs $8.60 and toppings are $1.10 each, how much would a 14" pizza with sausage, onion and mushrooms cost?  
If a 16" Cheese Pizza costs $10.55 and toppings are $1.30 each, how much would a 16" pizza with black olives, pineapple and green peppers cost? 