440. Calculating the Size of a Sefer Torah - part 2
Tefillin, Mezuzah v’Sefer Torah 9:6
After writing the sample column of text, he measures the column with his measuring stick. He then adds the two thumb-widths between columns and he calculates the number of columns the entire roll will take if he writes consistently in the same size. Once he knows the total number of columns, he calculates whether the entire Torah will fit in the number of columns in the roll based on the size of his hand-writing. If it will fit, he continues writing as per his sample text; if he calculates that there are more columns than necessary, he should write his letters wider. He writes another sample column of text to test this. If he calculates that there are fewer columns than necessary, he should write narrower letters; he writes another sample column of text to test it.
Tefillin, Mezuzah v’Sefer Torah 9:7
After determining the width of the column and the size of his penmanship, he takes the roll of parchment and divides each sheet into columns based upon the sample column that he wrote, scoring lines in each column. If more than three or four finger-widths remain after the last column, then he leaves just a thumb-width, plus the space needed to sew and cut. One need not be concerned that additional sheets of parchment might have to be added to make up for what gets cut off; the size of the writing will only require adding according to the number of columns he already calculated.