Flat Rate Envelope
Legal Flat Rate Envelope
Padded Flat Rate Envelope
Small Flat Rate Box
Medium Flat Rate Box
Large Flat Rate Box
APO/FPO/DPO Large Box
Retail (Post Office Counter)
Commercial Base (Online Rates)
Selected Service:Priority Mail Flat Rate
Package Size:Small Flat Rate Box
Pricing Tier:Retail
Weight Limit:Up to 70 lbs
Estimated Dimensions:8 5/8″ x 5 3/8″ x 1 5/8″
Total Postage Cost:$0.00
Online Savings:$0.00
About Flat Rate Shipping Costs
USPS Priority Mail® Flat Rate shipping is one of the most popular shipping options for e-commerce businesses and individuals because it simplifies the calculation process. "If it fits, it ships"® is the motto, meaning the weight of the package (up to 70 lbs) and the destination (within the domestic US) do not affect the price.
However, the cost does vary depending on two main factors: the size of the box and where you buy the postage.
Retail vs. Commercial Pricing
Our calculator compares two distinct pricing tiers:
Retail Rates: These are the prices you pay if you walk into a physical Post Office location to buy your label. They are the standard base prices.
Commercial Base Rates: These are discounted rates available through online postage software (like Stamps.com, Pirate Ship, or eBay shipping labels). These rates are significantly cheaper, often saving you between 10% to 20%.
Box Dimensions Reference
Box/Envelope Type
Inside Dimensions (Inches)
Retail Price (Est. 2024)
Flat Rate Envelope
12 1/2″ x 9 1/2″
$9.85
Padded Envelope
12 1/2″ x 9 1/2″
$10.60
Small Box
8 5/8″ x 5 3/8″ x 1 5/8″
$10.40
Medium Box (Top Loading)
11″ x 8 1/2″ x 5 1/2″
$18.40
Large Box
12″ x 12″ x 5 1/2″
$24.75
Weight and Restrictions
All Domestic Priority Mail Flat Rate boxes have a maximum weight limit of 70 lbs. While you do not need to weigh the package to determine the cost, you must ensure it does not exceed this limit. Additionally, the box contents must be secure, and the box must close completely flat without modification to the shape.
function calculateFlatRate() {
// Get Inputs
var packageType = document.getElementById('packageType').value;
var pricingModel = document.getElementById('pricingModel').value;
var resultBox = document.getElementById('resultOutput');
// Define Pricing Structure (Based on approx 2024 USPS Rates)
// Format: [Retail Price, Commercial Price]
var prices = {
'envelope': [9.85, 8.05],
'legal': [10.15, 8.35],
'padded': [10.60, 8.80],
'small': [10.40, 8.55],
'medium': [18.40, 14.75],
'large': [24.75, 19.90],
'large_apo': [23.00, 19.90] // APO often has retail discount
};
// Define Dimensions
var dimensions = {
'envelope': '12 1/2″ x 9 1/2″',
'legal': '15" x 9 1/2″',
'padded': '12 1/2″ x 9 1/2″',
'small': '8 5/8″ x 5 3/8″ x 1 5/8″',
'medium': '11" x 8 1/2″ x 5 1/2″ (or Side Loading)',
'large': '12" x 12″ x 5 1/2″',
'large_apo': '12" x 12″ x 5 1/2″'
};
// Define Readable Names
var names = {
'envelope': 'Flat Rate Envelope',
'legal': 'Legal Flat Rate Envelope',
'padded': 'Padded Flat Rate Envelope',
'small': 'Small Flat Rate Box',
'medium': 'Medium Flat Rate Box',
'large': 'Large Flat Rate Box',
'large_apo': 'APO/FPO Large Box'
};
// Calculate
var selectedData = prices[packageType];
var cost = 0;
var savings = 0;
if (pricingModel === 'retail') {
cost = selectedData[0];
// Calculate potential savings if they switched
savings = selectedData[0] – selectedData[1];
} else {
cost = selectedData[1];
// Calculate actual savings achieved
savings = prices[packageType][0] – prices[packageType][1];
}
// Display Data
document.getElementById('dispPackage').innerHTML = names[packageType];
var tierName = (pricingModel === 'retail') ? "Retail (Post Office)" : "Commercial Base (Online)";
document.getElementById('dispTier').innerHTML = tierName;
document.getElementById('dispDimensions').innerHTML = dimensions[packageType];
document.getElementById('dispCost').innerHTML = "$" + cost.toFixed(2);
// Handle Savings Display
var savingsRow = document.getElementById('savingsRow');
var savingsVal = document.getElementById('dispSavings');
if (savings > 0) {
savingsRow.style.display = 'flex';
if (pricingModel === 'retail') {
document.querySelector('#savingsRow .result-label').innerHTML = "Potential Online Savings:";
document.querySelector('#savingsRow .result-label').style.color = "#d9534f"; // Redish/Orange for missed opportunity
savingsVal.style.color = "#d9534f";
} else {
document.querySelector('#savingsRow .result-label').innerHTML = "Savings vs Retail:";
document.querySelector('#savingsRow .result-label').style.color = "green";
savingsVal.style.color = "green";
}
savingsVal.innerHTML = "$" + savings.toFixed(2);
} else {
savingsRow.style.display = 'none';
}
// Show Result
resultBox.style.display = 'block';
}