This is a good overview:

http://reference.jumpingmonkey.org/programming_languages/objective-c/types.html

or run this code

NSLog(@"Primitive sizes:");
NSLog(@"The size of a char is: %d.", sizeof(char));
NSLog(@"The size of short is: %d.", sizeof(short));
NSLog(@"The size of int is: %d.", sizeof(int));
NSLog(@"The size of long is: %d.", sizeof(long));
NSLog(@"The size of long long is: %d.", sizeof(long long));
NSLog(@"The size of a unsigned char is: %d.", sizeof(unsigned char));
NSLog(@"The size of unsigned short is: %d.", sizeof(unsigned short));
NSLog(@"The size of unsigned int is: %d.", sizeof(unsigned int));
NSLog(@"The size of unsigned long is: %d.", sizeof(unsigned long));
NSLog(@"The size of unsigned long long is: %d.", sizeof(unsigned long long));
NSLog(@"The size of a float is: %d.", sizeof(float));
NSLog(@"The size of a double is %d.", sizeof(double));

NSLog(@"Ranges:");
NSLog(@"CHAR_MIN:   %c",   CHAR_MIN);
NSLog(@"CHAR_MAX:   %c",   CHAR_MAX);
NSLog(@"SHRT_MIN:   %hi",  SHRT_MIN);    // signed short int
NSLog(@"SHRT_MAX:   %hi",  SHRT_MAX);
NSLog(@"INT_MIN:    %i",   INT_MIN);
NSLog(@"INT_MAX:    %i",   INT_MAX);
NSLog(@"LONG_MIN:   %li",  LONG_MIN);    // signed long int
NSLog(@"LONG_MAX:   %li",  LONG_MAX);
NSLog(@"ULONG_MAX:  %lu",  ULONG_MAX);   // unsigned long int
NSLog(@"LLONG_MIN:  %lli", LLONG_MIN);   // signed long long int
NSLog(@"LLONG_MAX:  %lli", LLONG_MAX);
NSLog(@"ULLONG_MAX: %llu", ULLONG_MAX);  // unsigned long long int

When run on an iPhone 3GS (iPod Touch and older iPhones should yield the same result) you get:

Primitive sizes:

The size of a char is: 1.
The size of short is: 2.
The size of int is: 4.
The size of long is: 4.
The size of long long is: 8.
The size of a unsigned char is: 1.
The size of unsigned short is: 2.
The size of unsigned int is: 4.
The size of unsigned long is: 4.
The size of unsigned long long is: 8.
The size of a float is: 4.
The size of a double is 8.
Ranges:
CHAR_MIN:   -128
CHAR_MAX:   127
SHRT_MIN:   -32768
SHRT_MAX:   32767
INT_MIN:    -2147483648
INT_MAX:    2147483647
LONG_MIN:   -2147483648
LONG_MAX:   2147483647
ULONG_MAX:  4294967295
LLONG_MIN:  -9223372036854775808
LLONG_MAX:  9223372036854775807
ULLONG_MAX: 18446744073709551615