| double | | double | double | float | float64 | double | float | Float |
| float | | float | float | float | float32 | float | float | Float |
| int32 | Uses variable-length encoding. Inefficient for encoding negative numbers – if your field is likely to have negative values, use sint32 instead. | int32 | int | int | int32 | int | integer | Bignum or Fixnum (as required) |
| int64 | Uses variable-length encoding. Inefficient for encoding negative numbers – if your field is likely to have negative values, use sint64 instead. | int64 | long | int/long | int64 | long | integer/string | Bignum |
| uint32 | Uses variable-length encoding. | uint32 | int | int/long | uint32 | uint | integer | Bignum or Fixnum (as required) |
| uint64 | Uses variable-length encoding. | uint64 | long | int/long | uint64 | ulong | integer/string | Bignum or Fixnum (as required) |
| sint32 | Uses variable-length encoding. Signed int value. These more efficiently encode negative numbers than regular int32s. | int32 | int | int | int32 | int | integer | Bignum or Fixnum (as required) |
| sint64 | Uses variable-length encoding. Signed int value. These more efficiently encode negative numbers than regular int64s. | int64 | long | int/long | int64 | long | integer/string | Bignum |
| fixed32 | Always four bytes. More efficient than uint32 if values are often greater than 2^28. | uint32 | int | int | uint32 | uint | integer | Bignum or Fixnum (as required) |
| fixed64 | Always eight bytes. More efficient than uint64 if values are often greater than 2^56. | uint64 | long | int/long | uint64 | ulong | integer/string | Bignum |
| sfixed32 | Always four bytes. | int32 | int | int | int32 | int | integer | Bignum or Fixnum (as required) |
| sfixed64 | Always eight bytes. | int64 | long | int/long | int64 | long | integer/string | Bignum |
| bool | | bool | boolean | boolean | bool | bool | boolean | TrueClass/FalseClass |
| string | A string must always contain UTF-8 encoded or 7-bit ASCII text. | string | String | str/unicode | string | string | string | String (UTF-8) |
| bytes | May contain any arbitrary sequence of bytes. | string | ByteString | str | []byte | ByteString | string | String (ASCII-8BIT) |