PackOS Checkout

Your checkout is quoting the wrong box.

Shopify's carrier-calculated rates never decide which box the order ships in, so dimensional weight is a guess and the quote misses. PackOS Checkout runs a real 3D bin-packing engine across your own box library, picks the box the order will actually ship in, and quotes live USPS, UPS and FedEx rates for that box. Shopify today — WooCommerce and other platforms coming soon.

Get PackOS Checkout View pricing

14-day free trial on every plan · full access · cancel any time

Checkout platforms: Shopify today · WooCommerce and other platforms coming soon
Setup time: Minutes, no code
Developer required: No

Illustration of six items, a hoodie, sneakers, a bottle, a small box, a cap and sunglasses, flowing into one transparent box drawn with its dimensions and marked as the right size for the order. — Checkout: many items, one box, one rate

The problem

Your checkout shipping is almost certainly wrong

Three things silently bleed margin on every merchant's checkout. Checkout fixes all three.

The problem
Flat-rate shipping silently loses moneyA $7 flat rate covers a 1 lb order — and loses you $4 on a 5 lb one. Across a year of orders, the losses quietly eat entire percentage points of margin.
Overcharging silently loses customersShipping sticker shock is the #1 cause of cart abandonment. Customers abandon at checkout without you ever seeing why — the order simply never happens.
Carrier-calculated rates still get it wrongShopify's native carrier rates use the wrong box because nothing is choosing the box for each order. Dimensional weight pricing turns a 2 lb order into a 23 lb charge.

Real bin-packing across your box library

Every order at checkout runs through a 3D bin-packing algorithm that tests your box sizes and picks the optimal one — so the rate quote matches the box you'll actually use.

What's inside Checkout

A real engine — not a rate estimator

Most "shipping apps" are thin wrappers around carrier APIs. Checkout is the bin-packing layer your checkout was missing.

What's inside Checkout
Live multi-carrier rate lookupQueries USPS, UPS, and FedEx simultaneously with the selected box dimensions and order weight. Returns live rates in real time — not estimates, not averages.
Split shipment logicIf an order is too large for any single box, PackOS Checkout splits it across multiple packages and quotes the total accurately. No under-quoting on big orders.
Native Shopify integrationRegisters as a Shopify carrier service and works at checkout immediately after install — no manual configuration required. WooCommerce and other platforms coming soon.

Rules and analytics

Margin analytics built inEvery quoted rate is logged. When the label is bought, the actual cost is compared to the quote. Your shipping margin — the number most merchants never track — is visible per order and per month.
No-code configurationBox library, carrier accounts, and handling fees are all managed in the PackOS dashboard. No developer required. No theme code to touch. Changes go live in seconds.

How Checkout works

Four steps from install to accurate rates

01
Install and authorize
Add PackOS Checkout from the Shopify App Store. Authorize read access to your product catalog and write access to checkout rates. Two minutes.
02
Add your box library
Enter the boxes you actually ship in. Dimensions, weights, and any special rules. Most merchants have 4–12 boxes and take under 15 minutes. PackOS Checkout auto-detects common shipping supplies.
03
Rates go live at checkout
From the moment install completes, customers see real carrier rates based on their order's optimal box — calculated live, per order. No estimates. No surprises.
04
Watch your margin recover
Track the delta between quoted rates and actual label costs in your dashboard, order by order, from the first day.

Who it's for

PackOS Checkout is built for you if…

You're a Shopify merchant shipping physical goods
You ship orders with varied item sizes, weights, or box choices
You suspect your flat-rate or weight-based shipping is losing you money
You want accurate live carrier rates at checkout — not estimates
You want the first platform to show you what shipping actually costs you

The margin loop

Close the gap between quote and label with PackOS Labels

Checkout quotes the rate. Labels buys the label — at that rate. When you use both, there's no silent margin leak between the price your customer saw and what actually hits your wallet. Every order ships at a tracked margin.

One order · Two numbers · One difference

Quoted at checkout

What the customer paid you to ship it

PackOS Checkout

Paid for the label

What the carrier charged you to move it

PackOS Labels

Margin

The difference, recorded on every order

Both products, on the same record

Run either product on its own. Run both and the same order carries both numbers.

Learn about Labels See Checkout + Labels together

Common questions about Checkout

How does PackOS Checkout know which box to quote?

You load your box library into PackOS Checkout — the same boxes you actually use to pack orders. When a customer checks out, PackOS runs a 3D bin-packing algorithm across the cart items and picks the optimal box. That box's dimensions are what gets sent to the carriers for the rate quote.

Does PackOS Checkout work with carrier-calculated rates I already have?

PackOS Checkout replaces native carrier-calculated rates with more accurate versions. It registers as a Shopify carrier service (WooCommerce and other platforms coming soon). You can keep other rate sources enabled; PackOS Checkout quotes against the box the order will actually ship in.

What if I don't have my product dimensions entered?

PackOS Checkout prompts you to add dimensions and weights for your top products during onboarding. The platform works best when your most-ordered products have accurate dimensions — but it handles missing data by falling back to sensible defaults until you fill them in.

How is this different from dimensional weight estimation?

Dimensional weight estimation guesses the DIM weight of an order. PackOS Checkout selects the exact box an order will ship in, then calculates DIM weight from that box's real dimensions — not an estimate. The difference: a 2 lb item in a wrong-sized box can be billed as 23 lbs. PackOS Checkout eliminates that gap.

Do I need PackOS Labels to use PackOS Checkout?

No. PackOS Checkout works standalone — you can keep buying labels wherever you buy them today. However, using PackOS Labels alongside Checkout means the rate your customer saw at checkout is the rate you pay for the label. No margin leak between quote and label.

Protect your margin at checkout

Add PackOS Checkout to your Shopify store and see accurate rates on your next order.

Get PackOS Checkout Or start with PackOS Labels — free

14-day free trial on every plan
Cancel any time