1
Create the product priced per unit of length
Add the product with a price equal to your rate per billing
unit — $0.75 per inch, say — and a single variant. The quantity
the customer buys will be the inches of film.
2
Find the quantity input
On the product page, inspect the quantity field. In Dawn it is
input[name="quantity"]; other themes use ids such as
#quantity or #Quantity-…. Copy a selector that matches exactly
one input.3
Create the design
Designs → Create New Design → Gang Sheet. Set the film, set
Bill per to the unit your price is in (inch here), and under
Pricing paste the selector into Price target. Optionally
set Price display source to the selector of the element
showing the line total, if your theme has one; leave it empty
otherwise.
4
Assign and test
Assign the design to the product and open the builder. As the
sheet packs, the theme’s quantity field changes to the billed
length, and the theme’s own price logic follows. Save, add to cart:
the cart shows 13 × $0.75 for a 13” sheet.
What this path cannot do
- Length tiers and setup fees. The store multiplies; it does not know about breaks or floors. Use Print Options for those.
- Server-side verification. The price is whatever the store computes from the quantity in the cart.
- Fixed sheet lengths work: the builder sends the sheet count, and the product is priced per sheet.