A 12 by 18 inch metal sign and a 36 by 48 inch one can be the same Shopify product. They don't weigh the same. Appify Custom Product Options works the shipping weight out from what the customer chose, using a weight formula you set once per calculator.
The calculated weight is saved with the order. Shipping apps and Shopify's built-in shipping calculator can then use it to work out the rate.
Where is the weight set?
In the calculator editor, open Optional Features, then Weight calculation. There are three parts.
- Weight formula. The rule that turns the customer's choices into a weight.
- Unit. lb, oz, kg or g.
- Computed weight. A live readout under the formula, worked out from the choices in your preview. Change a size in the preview and watch it move.
The weight formula uses the same building blocks as a price formula. It can read a size the customer typed, a choice they picked, a pricing variable or a row from a table.
What does a weight formula look like?
Two examples from the weight calculation guide cover most products.
Weight from size: a metal sign
Each square inch of the sign weighs 0.05 lb. The formula multiplies width by height by that figure:
INPUT("WIDTH") * INPUT("HEIGHT") * 0.05
A 12 by 18 inch sign comes to 10.8 lb. Type 36 by 48 and the weight follows. Nobody has to look it up by hand.
Weight from a choice plus a count: packaging with inserts
Here the box weight comes from a small table keyed by box size, and every insert adds 0.1 kg:
TABLE("box_weights", OPT_TOKEN("SIZE")) + INPUT("INSERT_COUNT") * 0.1
Choose a bigger box or add inserts, and the weight goes up with them.
The pattern is the same for any product: what one unit weighs, times how many or how big, plus anything that adds weight on its own.
Use one number for the price and the weight
Many products are priced and shipped off the same measurement. Work it out once and use it twice.
A pricing variable holds a named value, such as UNIT_WEIGHT read from a table by size, or VOLUME from length, width and height. The price formula and the weight formula can both read it.
- One place to update. Change the table row and the price and the weight both follow.
- Shorter formulas. Each step gets a name you can read, so the weight formula stays one line.
If you already price by volume, the same variable can drive the weight. The custom boxes and packaging guide works out that VOLUME variable for a box.
Examples by product
| Product | What changes the weight | Formula shape |
|---|---|---|
| Metal or acrylic signs | Width and height | Area times weight per square inch |
| Signs in several materials | Size and material | Area times a weight looked up by material |
| Boxes and packaging | Box size and inserts | Box weight from a table plus weight per insert |
| Packs sold by count | How many pieces | Count times the weight of one piece |
When the weight is the thing being sold, such as bulk food or metal by the pound, a Weight option lets the customer type the amount with a unit. Price and shipping weight can both read it.
Let the customer see the weight
If the weight matters to your buyers, put it in front of them. There are three places for it.
- On the calculator. A Calculation display shows a formula result in your own wording, such as "Estimated weight: {value} lbs".
-
In the price summary. Add the variable to the price summary, turn off price formatting and give it a template such as
{result} kg. It shows as a plain number beside the price lines. - On the order. In Cart properties, add the variable under a name customers understand. It appears on the cart line with the other choices.
Once it is a cart property, it can also print on emails and packing slips. That setup is in how to show custom options on order emails and packing slips.
What happens on reorders and restored carts?
The weight comes back with the product. When a customer reorders, or restores an abandoned cart, the shipping weight is recreated as the product is added back. Nobody has to fix it by hand.
Customers can also change their choices from the cart with Edit options, without starting over. More on that in how to let customers edit configured products in the Shopify cart.
Check it before you go live
- Weigh two real orders. Pick a small and a large configuration you have shipped before. Set them in the preview and compare the computed weight with your scale.
- Open Troubleshoot if it's off. The weight formula has the same Troubleshoot tab as a price formula, with each value worked through step by step.
- Place a test order. Confirm your shipping rates react to a heavy configuration the way you expect.
Pricing the same product by size is its own job. If that's next, how to price custom signs by size, material and quantity and setting up formula pricing step by step cover it.
FAQ
Can Shopify shipping weight change with the options a customer picks?
Yes, with Appify Custom Product Options. A weight formula works out the weight from the customer's choices, and the result is saved with the order for your shipping setup to use.
Which units can the weight use?
Pounds, ounces, kilograms or grams. You pick the unit next to the formula.
Can the price and the weight share a value?
Yes. Put the shared value in a pricing variable, such as a weight per unit read from a table, and reference it in both formulas.
Can customers see the weight before they buy?
Yes. Show it with a Calculation display on the calculator, as a line in the price summary, or as a cart property on the order.
Do I need a shipping app?
Not necessarily. Shopify's built-in shipping calculator can use the calculated weight, and so can shipping apps.
Every size ships at its own weight.
Whatever you sell, however you price it · The last options app you'll shop for