🧩Golang Type Memory Representation Quick Reference

This article may be updated and improved later

This article provides a quick reference for Go types and their actual memory representation. Instead of focusing on syntax or usage, it explains what happens under the hood when you create a value of each type — how it is stored in memory, its internal structure, and its size on 32-bit and 64-bit architectures.

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Pointer

• What is: Memory address pointing to another value.

unsafe.Pointer
*int, *string ...

• Memory:
  • 64-bit -> 8 bytes
  • 32-bit -> 4 bytes
• Note: A pointer can be nil, meaning it points to nothing.

---

String

• What is: Pointer to its underlying Bytes + len

type StringHeader struct {
    Data uintptr
    Len  int
}

• Memory: A pointer + int
  • 64-bit -> 8 + 8 = 16 bytes
  • 32-bit -> 4 + 4 = 8 bytes

---

Int, Float, complex(real + imaginary floats) or uint

If a numeric type is not explicitly sized (for example int or uint), its size depends on the architecture — 32-bit or 64-bit.

If the type is explicitly sized (int8, int64, complex64, etc.), its memory size matches the type name.

For example:

• int → 4 bytes on 32-bit, 8 bytes on 64-bit

• complex64 → 8 bytes (two float32 values)

---

Slice

• What is: Pointer to its underlying Bytes + len + cap

type SliceHeader struct {
    Data uintptr
    Len  int
    Cap  int
}

• Memory:
  • 64-bit -> 8 + 8 + 8 = 24 bytes
  • 32-bit -> 4 + 4 + 4 = 12 bytes
• Note: Nillable. A slice is nil when its data pointer is nil and both len and cap are zero.

---

Map

• What is: Pointer to the struct hmap(no_swiss) (maps.Map for the swiss)
• Memory:
  • 64-bit -> 8 bytes
  • 32-bit -> 4 bytes
• Note: Nillable (It is a Pointer)

---

Chan

• What is: Pointer to the struct hchan
• Memory:
  • 64-bit -> 8 bytes
  • 32-bit -> 4 bytes
• Note: Nillable (It is a Pointer)

---

Struct

• What is: Inline layout of its fields. If it has no fields, it occupies zero bytes.
• Memory: Sum of field sizes + alignment padding. which are 8 bytes or 4 bytes ( based on the architecture)

type Example struct {
    A int8   // 1 byte
    B int32  // 4 bytes
}

In the above example, the total size will be 8 bytes (on 64-bit) due to alignment padding.

type Example2 struct {
    A int64  // 8 bytes
    B bool   // 1 Bytes
}

Example2 will occupy 16 bytes on a 64-bit system.

---

Interface

• What is: Two Pointers(Type info pointer + data pointer)

type EmptyInterface struct {
    Type *Type
    Data unsafe.Pointer
}

type NonEmptyInterface struct {
    ITab *ITab
    Data unsafe.Pointer
}

• Memory:

  • 64-bit -> 8 + 8 = 16 Bytes
  • 32-bit -> 4 + 4 = 8 Bytes

• Note: Nillable. An interface is nil when both its type and data pointers are nil.

---

Func

• What is: Pointer to the function's code in memory.
• Memory:
  • 64-bit -> 8 Bytes
  • 32-bit -> 4 Bytes
• Note: Nillable, (It is a Pointer).

---

Category	Type	Size (64-bit)	Size (32-bit)	Note
Boolean	bool	1 byte	1 byte	Represents true or false. May include padding in structs.
Integer (Signed)	int8	1	1	8-bit signed integer.
	int16	2	2	16-bit signed integer.
	int32	4	4	32-bit signed integer.
	int64	8	8	64-bit signed integer.
	int	8	4	Machine word-sized integer (depends on architecture).
Integer (Unsigned)	uint8	1	1	8-bit unsigned integer (alias: byte).
	uint16	2	2	16-bit unsigned integer.
	uint32	4	4	32-bit unsigned integer.
	uint64	8	8	64-bit unsigned integer.
	uint	8	4	Machine word-sized unsigned integer.
	uintptr	8	4	Unsigned integer large enough to store a pointer.
Text Types	string	16	8	Struct: pointer to data + length (Data uintptr, Len int). Immutable.
	rune	4	4	Alias for int32, represents a Unicode code point.
	byte	1	1	Alias for uint8, represents a raw byte.
Floating Point	float32	4	4	32-bit IEEE 754 floating-point number.
	float64	8	8	64-bit IEEE 754 floating-point number.
Complex Numbers	complex64	8	8	Two float32 values: real + imaginary (4 + 4).
	complex128	16	16	Two float64 values: real + imaginary (8 + 8).
Composite Types	array	varies	varies	Fixed-length, contiguous block of elements. Value type.
	slice	24	12	Struct: pointer + length + capacity (Data uintptr, Len int, Cap int). Reference type.
	struct	varies	varies	Inline fields + alignment padding. Value type.
	map	8	4	Pointer to runtime.hmap (hash table). Reference type.
	chan	8	4	Pointer to runtime.hchan (channel buffer & state). Reference type.
	interface	16	8	Struct: type info pointer + data pointer (itab*, data unsafe.Pointer). Reference type.
	pointer (*T)	8	4	Direct memory address pointing to value of type T.
	function	8	4	Pointer to it's code.
Special Types	nil	—	—	Zero value for reference types. No memory allocation.
Unsafe / Runtime	unsafe.Pointer	8	4	Untyped pointer; can convert to/from uintptr.
Empty Struct	struct{}	0	0	Takes no space; used for signals or markers.