Per weight fees (kg, g, oz, lb)

Last updated: September 23, 2026

A Per weight fee multiplies your rate by weight, in the unit you choose: kilograms, grams, ounces or pounds. As a per-product fee it charges rate × unit weight × quantity for each matching product; as a cart fee it charges rate × the total cart weight. FlexiFees reads the weight set on each variant in Shopify and converts other units automatically.

Set it up

Make sure the products have a weight on each variant in Shopify. A variant without a weight counts as 0.
In the fee, set Fee type to Per weight, enter the rate, and pick the unit next to it: per kilogram, per gram, per ounce or per pound.
Choose Per product fee or Cart fee, add conditions, and publish.

FlexiFees fee form with fee type Per weight, 0.50 per ounce, as a per product fee

Per-product: rate × unit weight × quantity

Each matching product contributes its own weight times its quantity; the results are added into one fee line. Example: 0.50 per ounce on a 0.6 oz can, 10 cans: 0.50 × 0.6 × 10 = 3.00. Use product conditions or the product category condition to choose which products pay.

Cart fee: rate × total cart weight

Best for charges that follow the shipment. Example: 0.50 per ounce on a 12 oz cart = 6.00. Add a cart total weight condition (for example, at least 50 lb) so only heavy orders pay, as in the heavy order surcharge.

Details worth knowing

Any unit, either way. Your products can be weighed in grams while the rate is per pound; FlexiFees converts.
Small rates are fine. Rates accept four decimals, such as 0.0125 per gram.
Fee limits. Add a minimum or maximum. On a per-product fee they apply to the fee's total. A cart fee minimum applies even when the cart weighs 0.
Fee lines carry no weight, so the fee never inflates its own calculation or your shipping rates.
Existing fees keep working. Weight fees created before the unit choice existed keep charging per kilogram.
Need tiers or a per-started-kilogram rule? Use a Formula with weight_kg, weight_lb or cart_weight_lb.

The first cart with a new amount. Calculated fees produce amounts Shopify has not seen before. The first time a new amount appears, Shopify can take a few seconds, occasionally up to about a minute, to accept the new fee line; FlexiFees retries automatically, and the same amount is instant from then on. Fixed fees are prepared when you save and appear immediately.

Questions

What weight does the fee use?

The weight set on each variant in Shopify. Weights stored in grams, kilograms, ounces or pounds are converted to the unit of your rate automatically, and quantities are respected. A variant without a weight counts as 0.

Can I charge per ounce or per pound?

Yes. Pick per kilogram, per gram, per ounce or per pound next to the rate. Rates accept four decimals, for example 0.0125 per gram.

Can I charge the weight fee only above a threshold?

Yes. Add a cart total weight condition, for example is greater than or equal to 50 lb, so light orders pay nothing.

Can I limit the fee to certain heavy products?

Yes. Make it a per-product fee and add product conditions such as product category, collection, type or tag; only the matching products are weighed.

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