Size Price Calculator for OpenCart — price by size: per m², running metre, m³

Size Price Calculator for OpenCart sells products cut to size: curtains and blinds, glass and mirrors, fabric, carpet, worktops, profiles and cable, banners. The customer types the width, length or height on the product page, sees the price of exactly that size straight away, and the size travels with the order — into the cart, the checkout, the invoice, the e-mail and the admin.

The catalogue price of the product becomes the price per unit: put €24 and the “area” mode on a product, and a 120 × 200 cm piece (2.4 m²) costs €57.60. That is why OpenCart specials, quantity discounts and customer-group prices keep working unchanged: a special on the product is a special on every size of it. Units are mm, cm, m, inches or feet; the price is per m, m², m³ or ft, ft², ft³. The module does not edit core files; one licence covers three builds: OpenCart 4.x, 3.x and 2.3.

What the customer sees

• Size fields with hints. Under each field — the allowed range (“10–300 cm”); the fields come pre-filled, so the price is visible at once.
• The price while typing. The calculator box shows the price per m², the area charged, the price of one piece and of the quantity — in the shop’s currency and with its taxes. The server calculates it with the same code as the cart, so the cart shows exactly this amount.
• A wrong size is obvious. Below the minimum, above the maximum or off the step — a message under the field (“Width: at least 10 cm”), the field is highlighted, the add-to-cart button does nothing.
• However customers type it. “120”, “120,5”, “120 cm” — all of it is 120 centimetres. The same size typed differently merges into one cart line.

In categories, search, specials and the product modules (“Featured”, “Bestsellers”, “Latest”) the module adds the unit next to the price — “per m²”, “per m”, “per m³”. Without it a customer reads “€24.00” as the price of the whole product. The label can be switched off in the settings.

What the admin gets

Extensions → Modules → Size Price Calculator, three tabs: Products, Settings and Licence.

• Products sold by size. Start typing a name or model, pick the product and the mode: area (width × length or width × height), length, perimeter, volume, and in Pro — a price table or a formula. The module puts the size options the product needs on it as required options.
• Size rules: units, minimum, maximum, step and pre-filled value for each size.
• Price rules: a minimum area charged (a 0.3 m² piece is charged as 0.5 m²), rounding of the measure, a fixed fee per piece (cutting, hemming), a minimum price per piece, surcharges of other options per unit or per piece, product weight × measure.
• “Try a size” — the price and the measure of any size before saving.
• A product list with mode, sizes and status; a product that needs Pro is marked “Needs Pro — not orderable”. “Clean up” removes the settings of deleted products.
• Settings: the price per unit in the calculator, the unit next to the price in lists, the area line in the cart, the SKU of a listed size, the module styles, the add-to-cart button selector for a custom theme.

Pro: price tables, formulas, discounts, size lists

• Width × height price table. Paste a grid from Excel: the first line holds the widths, the first column the heights. A size between two columns is charged at the next larger one; an empty cell means “not sold”.
• Formula. Variables W, L, H (sizes), A (area), P (perimeter), V (volume), M (measure charged), RATE (product price), OPT (option surcharges); functions min, max, round, ceil, floor, abs, sqrt, if. For example max(RATE * A, 15) + OPT — at least €15 a piece.
• Volume discounts: −5% from 10 m², −10% from 25 m² — from the area of one piece or of the whole cart line.
• Size lists. A size → its own SKU (shown in the cart and the order), its own price instead of the calculated one and its own stock: taken off when the order is processed and given back on cancellation. “Only the listed sizes” replaces the size fields with a choice from the list.
• No limit on the number of products sold by size.

How it works, step by step

1. You pick a product and a mode. The module creates (once) three OpenCart text options — Width, Length, Height — and puts the ones needed on the product.
2. On the product page the module adds hints under those fields and the calculator box; the box takes its price from the server, with the same calculation as the cart.
3. When the product is added to the cart, the server checks the size and turns what was typed into a number (“120,5 cm” → 120.5). A wrong size comes back with a message under the field.
4. OpenCart prices the cart line as always: the product price (with a special, a discount, a group price) plus option surcharges. The module takes that price as the rate per unit and replaces the line price with the price of the size. Sub-total, taxes and weight are summed exactly as the core sums them.
5. Everything uses that cart: the cart page, the mini-cart, the checkout, One Page Checkout, order-total modules. The order is saved with the size price and the Width, Length and Area options.
6. A size that became invalid (the rules changed, Pro ended) is marked in the cart line and not let through to payment — the module never sells such a product at the price of one metre.

How much it costs

Pro is UAH 990, one payment, a licence for good. No yearly payments. One licence per domain covers all three builds — OpenCart 4.x, 3.x and 2.3. Moving the shop to another domain — press “Detach” on the Licence tab of the old shop and activate the key on the new one.

Trial first, then pay. The 7-day free Pro trial starts with a button on the Licence tab, one trial per shop. After the trial the Pro data stays in the admin, and products that need Pro stop taking orders until Pro is back.

Under the hood

• No core edits. OpenCart events and (on 4.x) a startup action. The module wraps the cart that is already in the shop — the standard one or one replaced by another extension — and changes only the price of the lines of products sold by size.
• Sizes are ordinary OpenCart options. So they show up wherever OpenCart shows options, with no template edits, and stay in the orders for good.
• One calculation for everything. The calculator on the page, the cart and the check on adding are the same server code. The price cannot be changed in the browser.
• An invalid size is not sold at the rate. Such a line is marked out of stock, and while it is in the cart the checkout stops at the cart even in a shop that sells out-of-stock products.
• OpenCart 2.3 has no event order. If Option Specials or Option Combinations were installed after the module, on the very first request the module lets them go first and moves its own event behind them — the order of installation does not matter.
• Own tables: product settings, size lists, and a log of size stock taken per order line (so a cancellation gives stock back exactly once).
• Removal. Uninstalling removes the events, the size options from the module’s products and the options themselves when no other product uses them. Product settings stay in case of a reinstall. OpenCart deletes the module settings together with the licence key — after a reinstall the key has to be activated again.

How to install

1. OpenCart 4: Extensions → Installer → upload cc_sizeprice.ocmod.zip (do not rename the archive) and press Install. OpenCart 3: Extensions → Installer → cc_sizeprice-oc3.ocmod.zip. OpenCart 2.3: the 2.3 installer copies nothing without FTP set up, so copy the contents of the upload/ folder from cc_sizeprice-oc2.ocmod.zip to the shop root with your hosting file manager.
2. Extensions → Extensions → Modules → Size Price Calculator → Install, then Edit.
3. Settings tab: Status on. Save.
4. Products tab: start typing a product name, pick it, set the mode, units and size limits, check the price with “Try a size” and save.
5. Set the price per unit in the product form — say €24 per m² — and open the product in the shop: the calculator is already under the fields.
6. For Pro: paste the licence key from the e-mail after payment, or start the 7-day trial on the Licence tab.