Does USPS Charge by Weight, Size, or Both? (Complete 2023 Guide)

Shipping packages through the United States Postal Service (USPS) can be confusing, especially when it comes to how rates are calculated. Unlike some carriers that charge strictly by weight, USPS determines costs based on both weight and size depending on the shipping service selected.

In this comprehensive guide, we‘ll break down exactly how USPS calculates shipping charges in 2024 so you can better understand and estimate costs.

Overview of USPS Shipping Services

USPS offers several domestic shipping services for envelopes and packages within specific size and weight limits:

• First-Class Package Service: For packages up to 16 oz only. Charges by weight.
• Priority Mail: For packages up to 70 lbs. Charges by weight or dimensional weight, whichever is greater.
• Priority Mail Express: For urgent packages up to 70 lbs. Charges by weight or dimensional weight.
• Parcel Select Ground: For packages up to 70 lbs. Charges by weight or dimensional weight.

The last three services determine final rates based on the dimensional weight if packages exceed certain size thresholds, which we’ll explore in-depth next.

How Dimensional Weight Works with USPS

Dimensional (DIM) weight sets rates based on package size as well as weight. USPS and other major carriers use this calculation method to account for extra handling effort required for oversized items.

When Does Dimensional Weight Apply?

Dimensional pricing kicks in for Priority Mail, Priority Mail Express, and Parcel Select Ground packages when they exceed the following size thresholds:

• Priority Mail: Over 1 cubic foot (1,728 cubic inches)
• Priority Mail Express: Over 0.5 cubic feet (864 cubic inches)
• Parcel Select Ground: Over 1 cubic foot

So if your parcel’s volume exceeds those cubic inch limits, dimensional weight will determine the final shipping rate.

USPS Dimensional Weight Formula

USPS uses the following dimensional weight calculation:

Dimensional Weight = Length (in inches) x Width (in inches) x Height (in inches) / 194

Let‘s break this formula down into an example:

You have a Priority Mail package with dimensions 15" x 10" x 5", so:

15 x 10 x 5 = 750 cubic inches

Since this is over 1 cubic foot (1,728 cubic inches), dimensional weight applies.

Plug it into the formula:

Dimensional Weight = 15 x 10 x 5 / 194 = 38.7 lbs

So the dimensional weight here would be 38.7 lbs, much greater than the likely actual weight. USPS would charge you the dimensional rate.

When to Use Dimensional vs. Actual Weight

Dimensional weight sets pricing whenever it exceeds the actual weight of a package.

For example:

• Package dimensions: 24” x 15” x 12” (product inside weighs 10 lbs)
• Dimensional weight = 24 x 15 x 12 / 194 = 57.6 lbs

Since 57.6 lbs is heavier than the actual package weight (10 lbs), USPS would charge the higher dimensional rate.

Conversely, if the product was super dense and actually weighed 60 lbs, USPS would charge based on the lower actual weight instead of dimensional.

So in summary, USPS virtually “weighs” oversized packages and charges whichever weight calculation produces the greater result. This prevents carriers from losing money shipping overly large packages that weigh very little.

How Much Does USPS Charge per Pound?

Now that we’ve covered dimensional weight, let’s break down the actual 2023 USPS price-per-pound rates:

First-Class Package Service

Priority Mail

Rates continue increasing incrementally up to $64.60 for 35 lbs, then climb more steeply beyond that weight.

Note: Dimensional rates apply if over 1 cubic foot.

Priority Mail Express

Rates keep incrementally increasing up to $184.30 for 70 lbs based on weight brackets.

Note: Dimensional rates apply if over 0.5 cubic feet.

Parcel Select Ground

Follows an incremental price scale up to $143.40 for 70 lbs shipments.

Note: Dimensional rates apply if over 1 cubic foot.

Tips for Saving on USPS Shipping

Follow these tips to keep USPS shipping costs low when mailing packages:

• Know the threshold dimensions where dimensional weight kicks in for each service. Keeping boxes under these limits can prevent much higher rates.
• Compare Priority Mail Flat Rate vs. regular Priority Mail. The flat rates can provide better deals on heavy or oversized packages.
• Use USPS packaging when possible – their boxes and envelopes are specially designed to hit dimensional “sweet spots” for lower shipping rates.
• Weigh packages accurately so you select the right service level and don’t get overcharged at the post office. Include all packaging.
• Enter dimensions carefully when checking rates online or at self-service kiosks to avoid surprises. Round up fractions.

The Bottom Line

When shipping with USPS, cost depends on both package weight and size. Weight matters for smaller parcels while dimensional weight, determined by a package’s volume, becomes the pricing factor for oversized items.

Checking all service rates and options while following best practices for weighting, measuring, and packaging ensures you find the best USPS shipping value.