You do not give enough information, but if you want to know how much excipient you must use in determinate formulation, I suggest you to consult the Pharmaceutical Excipients Handbook. It all depends on your formulation, if its is a Tablet, capsule, suspensión, injectable solution...etc.

Excipients are added in order to obtain a handleable form. Then ,the amount of excipients depends on the formulation you chose.

Let consider, you have a specific batch of a tablet preparation..

Now,

1. Measure the average weight of your preparation by taking 20 tablets (or as recommended). Let, it is "X" mg

2. Finely ground those using mortar and pestle... and analyze the quantity of the active ingredient per tablet by using UV/HPLC or any authentic method. Let, the average quantity of the active is found "Y" mg

3. Now, minus the value "Y" from "X" i.e. Z = X - Y ; where Z represents the average weight of excipients (in mg) of your tablet preparation.

Actually there is no specific rules to measure the mean weight of excipients... But you may consider this as a trick to calculate the quantity. 

yes it is depends on your preparation and for  each and every excipient there is some limitation.plz refer handbook of excipents and particularly about any excipient you just ask i will provide information to you

for excipients there some ratio standar according to U.S.P to be apply :

for example : Disintegrants:

Starch: – concentration up to 5-20% of tablet weight

starch paste 5-25% gelatine solution 10-20%, gum acacia, tragacantha, 10-25% glucose syrup 50%, cellulose derivative polyvinylpyrrolidone 2% (PVP), PEG

Lubricants - (typically 0.3 – 2%)

Silica derivative- colloidal silica such as Cab-O-Sil, Aerosil in 0.25-3% conc

Glidants:

1. Talc (concentration 1-2 %).

2. Colloidal silica (0.2 %).

3. Corn Starch 5-10%