Measuring a scene
Take a page from a correctly formatted screenplay (Courier 12, standard margins). Scene 14 starts at the top of page 22 and ends a little under halfway down page 23. Page 22 is full, so that is 1. On page 23 the scene fills three bands, so that is 3/8. The scene is 1 3/8.
Scene 15 then runs from just below scene 14 to near the bottom of page 23, filling four bands: 4/8. Some ADs reduce that to 1/2, but most boards leave it as 4/8 so everything adds the same way. A two-line scene ("INT. CAR - NIGHT. Maya checks the mirror.") still counts as 1/8.
A useful check: the eighths on any page should add to 8/8. If page 23 has scene 14 at 3/8 and scene 15 at 4/8, there's 1/8 left for whatever comes next. If your total for a page is 9/8, one of the scenes is over-counted.
Adding eighths without mistakes
Add whole pages and eighths separately, then carry every 8/8 into a whole page. For a day with scenes at 2 3/8, 7/8, and 1 6/8:
- Whole pages: 2 + 0 + 1 = 3
- Eighths: 3 + 7 + 6 = 16/8, which is 2 whole pages
- Total: 3 + 2 = 5 pages
The same method works for a whole script. Spreadsheets tend to turn "2 3/8" into a date or a decimal, so either store the total in eighths (19 for 2 3/8) and convert at the end, or use the page count calculator.
Where eighths get misused
Eighths measure length on the page and say nothing about how long a scene takes to shoot. A 1/8 action line reading "The car flips." is a stunt day. So when the breakdown sheet records 1/8, the AD also notes stunts, special effects, or vehicles that change how long it takes.
Revised pages cause another problem. When the script moves from white to blue pages, an added line can push a scene from 5/8 to 6/8, and the change has to reach the strip and the day totals. There's a full walkthrough in how to calculate script page counts, and the totals roll up into the page count for each shoot day.
Storiara's Scenes module reads page lengths in eighths from the uploaded script, and you can correct any length by hand.