Integer Type Ranges

Reference exact-width integer ranges plus stdint.h limit macros and stddef.h size and pointer-difference types.

Use stdint.h when you need fixed-width integer typedefs and portable limit macros, then use stddef.h for object sizes and pointer differences. Exact-width typedefs are optional in the C standard, but when a platform provides them their limits are fixed and portable.

Exact-width types

stdint.h

int8_t, uint16_t, int32_t, uint64_t

Use these when the storage width must match a register, packet field, flash layout, or file format exactly.

At least N bits

stdint.h

int_least8_t, uint_least32_t

These give you the smallest available type that still guarantees at least the requested bit width.

Fastest at least N bits

stdint.h

int_fast8_t, uint_fast16_t

These trade exact width for the fastest integer type that still provides at least the requested number of bits.

Sizes and pointer deltas

stddef.h + stdint.h limits

size_t, ptrdiff_t, intptr_t, uintptr_t

Reach for these when you need object sizes, pointer subtraction results, or pointer-sized integer round-trips.

Exact-width ranges

Portable values for the exact-width integer typedefs commonly used in firmware, protocols, and packed binary formats.

Type	Header	Bits	Min	Max	Limit macros	Hex span
uint8_t	stdint.h	8	0	255	UINT8_MAX	0x00 - 0xFF
int8_t	stdint.h	8	-128	127	INT8_MIN / INT8_MAX	0x80 - 0x7F
uint16_t	stdint.h	16	0	65,535	UINT16_MAX	0x0000 - 0xFFFF
int16_t	stdint.h	16	-32,768	32,767	INT16_MIN / INT16_MAX	0x8000 - 0x7FFF
uint32_t	stdint.h	32	0	4,294,967,295	UINT32_MAX	0x00000000 - 0xFFFFFFFF
int32_t	stdint.h	32	-2,147,483,648	2,147,483,647	INT32_MIN / INT32_MAX	0x80000000 - 0x7FFFFFFF
uint64_t	stdint.h	64	0	18,446,744,073,709,551,615	UINT64_MAX	0x0000000000000000 - 0xFFFFFFFFFFFFFFFF
int64_t	stdint.h	64	-9,223,372,036,854,775,808	9,223,372,036,854,775,807	INT64_MIN / INT64_MAX	0x8000000000000000 - 0x7FFFFFFFFFFFFFFF

Related standard limits

Useful typedefs and macros from stdint.h and stddef.h when exact-width integers are not the best fit.

Type or family	Declared in	Limit macros	Guaranteed range	When to use it
int_leastN_t / uint_leastN_t	stdint.h	INT_LEASTN_MIN / INT_LEASTN_MAX / UINT_LEASTN_MAX	At least N bits	Smallest implementation type that meets the width guarantee.
int_fastN_t / uint_fastN_t	stdint.h	INT_FASTN_MIN / INT_FASTN_MAX / UINT_FASTN_MAX	At least N bits	Fastest implementation type that still meets the width guarantee.
intmax_t / uintmax_t	stdint.h	INTMAX_MIN / INTMAX_MAX / UINTMAX_MAX	Implementation-defined widest integer type	Good for generic parsing, formatting, and arithmetic across mixed integer widths.
intptr_t / uintptr_t	stdint.h	INTPTR_MIN / INTPTR_MAX / UINTPTR_MAX	Optional pointer-sized integer range	Optional typedefs for safely round-tripping a pointer value through an integer.
size_t	typedef in stddef.h, SIZE_MAX in stdint.h	SIZE_MAX	0 .. SIZE_MAX	Unsigned type returned by sizeof and commonly used for buffer, array, and object sizes.
ptrdiff_t	typedef in stddef.h, limits in stdint.h	PTRDIFF_MIN / PTRDIFF_MAX	PTRDIFF_MIN .. PTRDIFF_MAX	Signed type produced by subtracting two pointers into the same array object.