I assume you need this done in code?
This may not help a lot: you may have to tweak the row heights as well, as altering the cell font size does not affect that.
private void SetColumns()
{
float current = 5.0F;
foreach (DataGridViewColumn col in myDataGridView.Columns)
{
col.DefaultCellStyle.Font = new Font("Verdana", current);
current += 5.0F;
}
}