How to Do Ternary or Trinary, Base 3 Number System Conversions  Includes Examples
If you understand the everyday decimal (base 10) number system, then you already understand the ternary, base 3 counting and numbering system. You just don’t know you know yet. The complete lesson immediately follows the short semantics note about "ternary" versus "trinary".
How to Learn the Ternary Base 3 Numbering System
And a semantics note.
Semantics Note
Ternary is the primary descriptor used to identify base 3 (using the digits 0 1 2) in mathematics as relates to numbering systems.
Trinary is the primary descriptor used to identify base three as relates to logic (using the digits 1 0 +1); but the term has also been used in place of ternary. This page does not address the logic definition of trinary.
This page is about and explains the base 3 number system; usually called ternary, but sometimes referred to as trinary.
Complete Lesson and Examples
Quick review of base 10 structure...
Base 10, Decimal Orders of Magnitude
1 · 10 · 100 · 1,000 · 10,000 · 100,000
Positional
100,000 · 10,000 · 1,000 · 100 · 10 · 1
We use the base 10 numbering/counting system in our daytoday living. Base 10 has ten numbers (09) and orders of magnitude that are times ten.
 The lowestorder number represents itself times one.
 The nextorder number represents itself times 10.
 The next order number represents itself times 10 x 10, or itself times 100.
 The next order of magnitude would be 10 x 10 x 10, or 1000.
And so on.
A base 10 example would be the number 3528. This number means that there are:
 Eight 1’s,
 two 10’s,
 five 100’s,
 and three 1000's.
Which represents 8 + 20 + 500 + 3000; for a total of 3528.
The ternary or base3 numbering system...
Orders of Magnitude in Base 3
 1 · 3 · 9 · 27 · 81 · 243 · 729 · 2187 · 6561
Positional
 6561 · 2187 · 729 · 243 · 81 · 27 · 9 3 · 1
...uses the same structure, the only difference being the orders of magnitude. Base 3 or ternary has three numbers: 0, 1, and 2.
The orders of magnitude are times three.
 The lowestorder number represents itself times one.
 The nextorder number represents itself times 3.
 The next order number represents itself times 3 x 3, or itself times 9.
 The next order of magnitude would be 3 x 3 x 3, or itself times 27.
 The next order of magnitude would be 3 x 3 x 3 x 3, or itself times 81.
And so on.
A basic, first example of a ternary number would be the base 3 number 11111. This would mean there is:
 one 1,
 one 3,
 one 9,
 one 27,
 and one 81.
Which represents 1 + 3 + 9 + 27 + 81; for a total of 121 in Base 10 decimal.
Another base 3 example would be the number 1120. This number means that there are:
 No 1’s,
 two 3’s,
 one 9,
 and one 27.
Which represents 0 + 6 + 9 + 27; for a total of 42 in base 10 decimal.
Another base 3 example would be the number 2101. This number means there are:
 One 1,
 No 3's,
 One 9,
 And two 27’s.
Which represents 1 + 0 + 9 + 54; for a total of 64 in base 10 decimal.
More Ternary ( Base 3 ) to Base 10 Conversion Examples
Column headings in the following table are simply a convenience relist of the relevant positional orders of magnitude as applies to each column. There is no significance attached as to where one column ends and the next one begins.
9 3 1
 9 3 1
 27 9 3 1


0=0
 110=12
 220=24

1=1
 111=13
 221=25

2=2
 112=14
 222=26

10=3
 120=15
 1000=27

11=4
 121=16
 1001=28

12=5
 122=17
 1002=29

20=6
 200=18
 1010=30

21=7
 201=19
 1011=31

22=8
 202=20
 1012=32

100=9
 210=21
 1020=33

101=10
 211=22
 1021=34

102=11
 212=23
 1022=35

Orders of Magnitude in Base 3
 1 · 3 · 9 · 27 · 81 · 243 · 729 · 2187 · 6561
Positional
 6561 · 2187 · 729 · 243 · 81 · 27 · 9 3 · 1
(convenience relist)
Comments
Cool. Have you thought about a writeup of "balanced ternary"? The base is still three, but the digits are +0 instead of 012. So to represent 15, you use +0, that is, +27, 9, 3, +0.
This way you can represent negative numbers without needing any special notation like you would in regular ternary.