How to Set Shipping Rates for an Online Store

Shipping is where many small online stores quietly lose money. Charge too little and every order eats into your margin. Charge too much and shoppers leave at checkout. Extra costs like shipping are the top fixable reason for checkout abandonment in Baymard Institute’s research, cited by about 4 in 10 US shoppers who left a purchase, excluding people who were just browsing.

The answer isn’t a single magic number. It’s a pricing model that fits your products, your margins and what your customers expect. This guide compares the main options, explains dimensional weight in plain terms, and walks you through setting rates step by step.

The 4 main shipping rate models

Most online stores use 1 of these models, or a mix.

Many stores combine them. For example: free shipping over a set amount, a flat rate below it and calculated rates for oversized items.

Flat-rate shipping

Flat rate is the easiest to explain. “Shipping is $6.95 on every order” is clear, predictable and easy to show on product pages.

Flat rate works well when:

• Most of your products are similar in size and weight
• Your orders usually go out in 1 or 2 standard box sizes
• You want shoppers to know the shipping cost before checkout

To set a flat rate, look at what you actually paid to ship your last 50 to 100 orders. Use a figure near the average, then decide whether you’ll absorb some of the difference on long-distance or heavier orders.

Tiered flat rates are a useful upgrade. You charge by order value or weight band, such as one rate under 1 pound and another for 1 to 5 pounds. This keeps the simplicity while reducing losses on heavy orders.

Carrier flat-rate packaging, such as USPS Priority Mail Flat Rate boxes, can also make your own costs predictable for small, heavy items.

Real-time calculated shipping

Calculated shipping pulls live rates from carriers like USPS, UPS and FedEx at checkout, using the customer’s address and your package weight and dimensions. Most major ecommerce platforms support it, though availability can depend on your plan or require a shipping app.

Calculated rates work well when:

• Your products vary a lot in size and weight
• You sell heavy or bulky items where a flat rate would be wildly wrong
• You want shoppers to choose between speed options

The catch is accuracy. Calculated rates are only as good as the weights and dimensions you enter for each product and box. If you leave dimensions blank, your checkout may undercharge for bulky items that carriers bill by size.

Free shipping and free-shipping thresholds

Free shipping is never free. Someone pays for it, and that someone is you unless you build it into prices or order sizes.

Built-in free shipping means raising product prices to cover average shipping costs. It works best for light, compact, higher-margin products, where the shipping cost is a small share of the price.

Threshold free shipping means offering free shipping once the cart reaches a set value. It can encourage shoppers to add 1 more item to qualify. To set a threshold:

1. Find your average order value.
2. Set the threshold somewhat above it, so many shoppers need to add a little to qualify.
3. Check that the gross margin on an order at the threshold still covers shipping comfortably.
4. Show progress in the cart, such as “You’re $8 away from free shipping.”

Key takeaway: Choose the model your margins can support, then make the cost visible early. A fair shipping price shown on the product page beats a “cheap” one that surprises shoppers at checkout.

Dimensional weight explained

Dimensional weight, often called DIM weight, is how carriers charge for space, not just weight. A large, light box takes up as much truck space as a heavy one, so carriers bill for whichever is greater: the actual weight or the dimensional weight.

The basic formula is:

DIM weight (lb) = length x width x height (in inches) / divisor

The divisor depends on the carrier and rate type:

Always round as the carrier specifies. UPS and FedEx round the result up to the next whole pound, and USPS now rounds fractional inches up to the next whole inch before calculating. If you set up your shipping rules before mid-2026, recheck any USPS estimates for larger boxes, because the lower divisor raises their billable weight.

A worked example

Say you ship a candle set that weighs 3 pounds in a 12 x 10 x 8 inch box.

• Volume: 12 x 10 x 8 = 960 cubic inches
• UPS Daily Rates or FedEx: 960 / 139 = 6.9, which rounds up to 7 pounds billable
• USPS: the box is under 1,728 cubic inches, so USPS uses the actual 3 pounds

Now drop to a 10 x 8 x 6 inch box: 480 cubic inches, or 3.5 rounded up to 4 pounds at UPS or FedEx. A smaller box can cut your billable weight almost in half.

How to reduce dimensional weight costs

• Use the smallest box that protects the product.
• Stock 3 to 5 box sizes that fit your common orders instead of 1 big size.
• Use poly mailers for soft goods like clothing.
• Measure and enter dimensions for every product and box in your platform, so calculated rates are accurate.
• Compare carriers by package size. Our guide to USPS vs UPS vs FedEx for small sellers matches each carrier to package types.

Other costs to build into your rates

Postage isn’t your only shipping cost. Include these when you set prices:

• Packaging: boxes, mailers, tape, void fill and labels
• Carrier surcharges: residential delivery, fuel, peak-season and remote-area surcharges can apply, especially at UPS and FedEx
• Insurance for higher-value items
• Address corrections and returns
• Labor: the time it takes to pick, pack and label each order
• Fulfillment fees if you use a third-party logistics provider

Check each carrier’s current rate guide and surcharge list. Rates and surcharges typically change at least once a year.

Where to start: set your shipping rates in 7 steps

1. Pull your last 3 months of orders. Note package sizes, weights, destinations and what you paid.
2. Group your products into 3 or 4 size and weight bands.
3. Calculate billable weight for each band with each carrier, using the DIM formulas above.
4. Get real quotes using carrier calculators or your platform’s discounted rates. Many ecommerce platforms and shipping apps offer discounted carrier rates compared with retail counter prices.
5. Choose a model: flat, tiered, calculated, free or threshold. Most small stores start with threshold free shipping plus a flat rate below it.
6. Test the margin. For each band, check that product margin minus shipping and packaging still leaves a profit.
7. Show shipping early. Add a line like “Free shipping over $50, otherwise $5.95” on product pages and in the cart.

Then review every quarter. Watch your shipping cost as a share of revenue, your cart abandonment rate and your average order value. Our guide to retail analytics covers how to track these.

Shipping speed and expectations

Price isn’t the only thing shoppers weigh. Delivery that’s too slow is the second most common checkout abandonment reason in Baymard’s list. Show estimated delivery dates, not just service names, and consider offering 1 faster paid option.

Be careful about promises. The FTC’s Mail, Internet, or Telephone Order Merchandise Rule requires sellers to have a reasonable basis for any shipping time they state. If you don’t state a time, you must ship within 30 days. If you can’t ship on time, you must notify the buyer and give them the option to cancel for a prompt refund. This is not legal advice.

Your shipping and return terms work together, so make sure they’re consistent. See our guide on how to write a return policy and our checklist on why shoppers abandon carts.

Conclusion

The right shipping rates come from your own numbers: package sizes, real carrier costs and margins. Learn how dimensional weight affects your boxes, pick a model your margins can carry, and show the cost early so it never surprises anyone. Start with your last 3 months of orders, and you can have a better shipping setup live by next week.

Sources

• UPS: Shipping dimensions and weight — DIM divisors of 139 (Daily Rates) and 166 (Retail Rates), billable weight rules
• FedEx: What is dimensional weight? — 139 divisor and billable weight
• USPS: Ground Advantage — DIM weight for packages over 1 cubic foot, 139 divisor, rounding rules, 70-pound limit
• Federal Trade Commission: Business guide to the Mail, Internet, or Telephone Order Merchandise Rule — shipping time statements, 30-day rule, delay notices
• Baymard Institute: Cart abandonment rate statistics — extra costs and slow delivery as abandonment reasons