Why Shopify doesn't do it on its own
A Shopify product has up to 3 options and 2,048 variants, and each variant has one fixed price. Made-to-measure goods don't come in fixed sizes: a blind is priced from a grid of widths and drops, a rug or a glass panel by the square metre with a minimum charge, curtains by the metre of fabric. Shopify's checkout charges the variant's price. Changing a line's price in the cart takes a Shopify Function, and the simplest kind (updating a line) is open only to Shopify Plus stores and development stores.
The free way
- Size bands as variants. Make a Width option and a Drop option with your bands (600, 900, 1,200 mm…) and give every combination its grid price. The shopper picks the band at or above their size.
- Or price by area with the quantity. Set the variant's price to your price for 0.1 m², and tell the shopper to enter their area in tenths as the quantity (a 1.45 × 1.8 m blind is 2.61 m², so quantity 27).
- Collect the exact size. Add a "Width (mm)" and "Drop (mm)" field to the product form with your theme's custom fields or a free form app, so it lands on the order.
- Or quote by hand. Ask for the size on a contact form, work out the price, and send a draft order invoice.
Where the free way falls short
- Bands mean the shopper pays for the band, not their size, and a 10 × 6 grid is 60 variants per product colour.
- The quantity trick confuses shoppers, shows a strange quantity in the cart, and nothing stops a quantity of 1.
- Nothing checks that the size typed matches the price paid, or that a size was typed at all.
- Quoting by hand loses the shoppers who wanted to buy now.
- The shopper never sees how big their size really is.
The easier way: RNS Custom Size Calculator
- Set up a product in minutes. Pick roller blind, curtains, cushion, glass panel, tabletop, rug or another starting point, and paste your price grid from a spreadsheet, or set a price per m², per metre or your own sum, with minimums, rounding and extras.
- The shopper types their size in metric or imperial, inside or outside the recess, sees the item in 3D at that size, and the price updates on the Add to cart button.
- Shopify charges your price. The app's cart step works out each sized line from your saved rule in the cart and at checkout, using a Shopify Function. A line with no size is stopped at the cart and checkout, and every order is checked against your rule.
The Free plan covers 1 sized product with every price rule and the 3D. Pro is $19 a month for every product, with a 14-day free trial; Plus ($39) adds View in your room in AR.
What to know: the block replaces your theme's own price and Add to cart on sized products, and needs one Save in the theme editor.
Questions
Can a Shopify variant have a custom price?
No. Each variant has one fixed price. A different price per typed size needs an app that adjusts the cart line.
Can I keep my price grid?
Yes. Paste it from a spreadsheet; sizes round up to the next band, as on your price list.
Does it work with Shopify Markets?
Yes. The cart step converts your price at the market's rate, and the block shows numbers the way each storefront language writes them.
Sources
- Shopify Help: adding variants (3 options, 2,048 variants; checked 18 Oct 2026)
- Shopify Functions: Cart Transform (line update on Plus and development stores; checked 29 Oct 2026)