The NUMERICAL VALUE
(Source: The Universal History of Number, by Georges Ifrah)
The Arabs have frequently used a system of Numerical Notation in which each letter of their own alphabet has a specific numerical value. According to F. Woepke (1863  The Historian who is expert in the history of number), They " seem to have considered (this system) as uniquely and by preference their own".
Thy call this " huruf al jumal " (calculating the total) which means something like " totals means of letter"
Another name of Numerical Value is what they call JEWISH "GEMATRIA" (possibly a corruption of Greek geometrikos arithmos, geometrical number).
For my web, I'd prefer to use NUMERICAL VALUE (easy to understand) than Gematria.
Here is
THE TABLE OF ARABIC NUMERICAL VALUE
No 
LETTERS 
NUMERICAL VALUES 

1 
'Alif 
a 
1 

2 
Bã' 
b 
2 

3 
Tã' 
t 
400 

4 
Tsã' 
ts 
500 

5 
JÏm 
j 
3 

6 
Hã' 
h 
8 

7 
khã' 
kh 
600 

8 
dãl 
d 
4 

9 
dzãl 
dz 
700 

10 
rã' 
r 
200 

11 
zai 
z 
7 

12 
sïn 
s 
60 

13 
syïn 
sy 
300 

14 
shãd 
sh 
90 

15 
dhãd 
dh 
800 

16 
thã' 
th 
9 

17 
zhã' 
zh 
900 

18 
'ain 
'a 
70 

19 
ghain 
gh 
1000 

20 
fã' 
f 
80 

21 
qãf 
q 
100 

22 
kãf 
k 
20 

23 
lãm 
l 
30 

24 
mïm 
m 
40 

25 
nün 
n 
50 

26 
hã' 
h 
5 

27 
waw 
w 
6 

28 
yã' 
y 
10 
Example:
ALLAH
' Alif, lãm,lãm,hã'
' Alif = 1, lãm = 30, hã' = 5
ALLAH = 1+ 30+ 30+ 5 = 66
Total Numerical Value ALLAH
= 66
Combination of Numerical Value ALLAH
= 1 30 30 5

MUHAMMAD
mïm, Hã',mïm, dãl
mïm = 40, Hã' = 8, dãl =4
MUHAMMAD = 40+8+40+4 = 92
Total Numerical Value MUHAMMAD
= 92
Combination of Numerical Value MUHAMMAD
= 40 8 40 4