How to calculate the record length of an array of structure

I have the following structure:

Public Structure Aliment
              Public Alino As Integer
              <VBFixedString(83)> Public NomUS As String
              <VBFixedString(50)> Public NomFR As String
              <VBFixedString(24)> Public Categ As String
              Public Paramali() As Double
        End Structure

Then I have an array of this structure

Public TousALI() As Aliment

The array Paramali() is redimensioned:

ReDim Preserve TousALI.Paramali(80)

The data stored in the TousALI array, comes from a .txt file.
I load it, display it in a datagridview and it works perfectly.

But now I want to store the data in a random access file:

FileOpen(1, FileAliRand, OpenMode.Random, OpenAccess.Write, , 813)

But the next line :
FilePut(1, TousALI(I)) gives me an error: Incorrect record length.

the record lenght, 813 is the total number of bytes.

How to calculate the actual number of bytes of my array ?

Thanks for help

What I have tried:

I have tried many different length, but it doesn't work

Tags: Visual Basic