Postage Cost Calculator

Postage rates change regularly, so this calculator doesn’t pretend to know today’s prices. Instead, you enter the current rates from your post office’s price list — once — and it does the maths: letters by the ounce, large envelopes, parcels by actual or dimensional weight, and how many stamps to use.

What’s in the pack

• Mailing log spreadsheet that calculates postage from the rates you enter
• Shipping cost comparison worksheet for carriers and services
• Package measuring and dimensional weight worksheet
• Printable address label sheets and return-address labels
• Holiday card mailing checklist

Designed for home businesses, sellers and families sending lots of mail.

How postage is usually calculated

Always use the current official price list — postal services revise prices, often once or twice a year.

Weights and conversions

Postage is based on weight rounded up to the next whole unit — 1.1 oz counts as 2 oz — so a kitchen or postal scale saves money on heavier letters.

Dimensional weight

For large, light parcels, carriers may charge by size rather than actual weight. Dimensional weight = length × width × height (in inches) ÷ a divisor set by the carrier — 166 is commonly used by USPS for retail packages, while other carriers use different divisors, such as 139. You pay for whichever is greater, actual or dimensional weight. Using the smallest box that protects the item often lowers the price.

Worked example

A crafter mails a 2.5 oz card with a small gift. Using the current rates from the price list — say a first-ounce rate of a and an additional-ounce rate of b — the calculator rounds the weight up to 3 oz and shows the postage as a + 2b, then how many Forever stamps cover it. For a 14 × 12 × 10 in box weighing 4 lb, the box is 0.97 ft³, so dimensional weight (about 10.1 lb at a 166 divisor) may not apply with USPS; with a carrier that applies it to all boxes, the billable weight would be 11 lb.

International mail basics

• International letters and parcels are priced by weight and destination group, not by US zones.
• Parcels need a customs declaration describing the contents and value.
• Some items are prohibited or restricted in certain countries — check before sending.
• Delivery times vary widely; allow extra time around holidays.
• Tracking and insurance options differ from domestic services.

Measuring a package correctly

1. Measure the longest side as length.
2. Measure the other two sides as width and height.
3. Round each measurement up to the nearest whole inch, as carriers do.
4. Include bulges from overpacking.
5. Weigh the packed box on a scale and round up to the next pound.

Length plus girth (twice the width plus twice the height) also matters for oversized parcels — each carrier publishes its own limits.

Tips to save on postage

• Weigh items rather than guessing.
• Keep letters flat and flexible to avoid non-machinable surcharges.
• Use the smallest suitable box, and flat-rate boxes when they’re cheaper.
• Compare services and carriers for parcels.
• Print labels online — some carriers offer lower online prices than retail counters.

AI-assisted content

This guide and the templates were drafted with AI assistance and reviewed by Kedop. Postage rules and prices change — confirm with your postal service or carrier.