procedure DimensionarGrid(dbg: TDBGrid);
type
TArray = Array of Integer;
procedure AjustarColumns(Swidth, TSize: Integer; Asize: TArray);
var
idx: Integer;
begin
if TSize = 0 then
begin
TSize := dbg.Columns.count;
for idx := 0 to dbg.Columns.count - 1 do
dbg.Columns[idx].Width := (dbg.Width - dbg.Canvas.TextWidth('AAAAAA')
) div TSize
end
else
for idx := 0 to dbg.Columns.count - 1 do
dbg.Columns[idx].Width := dbg.Columns[idx].Width +
(Swidth * Asize[idx] div TSize);
end;
 
var
idx, Twidth, TSize, Swidth: Integer;
AWidth: TArray;
Asize: TArray;
NomeColuna: String;
begin
SetLength(AWidth, dbg.Columns.count);
SetLength(Asize, dbg.Columns.count);
Twidth := 0;
TSize := 0;
for idx := 0 to dbg.Columns.count - 1 do
begin
NomeColuna := dbg.Columns[idx].Title.Caption;
dbg.Columns[idx].Width := dbg.Canvas.TextWidth
(dbg.Columns[idx].Title.Caption + 'A');
AWidth[idx] := dbg.Columns[idx].Width;
Twidth := Twidth + AWidth[idx];
 
if Assigned(dbg.Columns[idx].Field) then
Asize[idx] := dbg.Columns[idx].Field.Size
else
Asize[idx] := 1;
 
TSize := TSize + Asize[idx];
end;
if TDBGridOption.dgColLines in dbg.Options then
Twidth := Twidth + dbg.Columns.count;
 
// adiciona a largura da coluna indicada do cursor
if TDBGridOption.dgIndicator in dbg.Options then
Twidth := Twidth + IndicatorWidth;
 
Swidth := dbg.ClientWidth - Twidth;
AjustarColumns(Swidth, TSize, Asize);
end;

procedure TForm1.FormResize(Sender: TObject);
begin
 
// É só informar o seu DBgrid
DimensionarGrid( GridProdutos );
end;