Estimate domestic postage costs for Letters, Flats, and Light Parcels.
Standard Letter (Envelope)
Metered Letter (Office)
Large Envelope (Flat)
First Class Package (Retail)
Max weight for Letters: 3.5 oz | Flats: 13 oz | Retail Parcels: 13 oz
Zone 1 (Local)
Zone 2 (0-150 miles)
Zone 3 (151-300 miles)
Zone 4 (301-600 miles)
Zone 5 (601-1000 miles)
Zone 6 (1001-1400 miles)
Zone 7 (1401-1800 miles)
Zone 8 (1801+ miles)
Zone 9 (Freely Associated States)
Distance affects price for packages only.
Estimated Postage:
$0.00
function toggleZoneDisplay() {
var type = document.getElementById("mailType").value;
var zoneGroup = document.getElementById("zoneGroup");
if (type === 'parcel') {
zoneGroup.style.display = 'block';
} else {
zoneGroup.style.display = 'none';
}
}
function calculatePostage() {
// Inputs
var type = document.getElementById("mailType").value;
var weight = parseFloat(document.getElementById("weightOz").value);
var zone = parseInt(document.getElementById("zoneSelect").value);
// Output elements
var resultBox = document.getElementById("resultBox");
var costDisplay = document.getElementById("costDisplay");
var breakdownDisplay = document.getElementById("breakdownDisplay");
var errorMsg = document.getElementById("errorMsg");
// Reset display
errorMsg.style.display = "none";
resultBox.style.display = "none";
// Basic Validation
if (isNaN(weight) || weight 3.5) {
errorMsg.innerHTML = "Standard letters cannot exceed 3.5 oz. Please select 'Large Envelope (Flat)' or 'Package'.";
errorMsg.style.display = "block";
return;
}
var base = (type === "letter") ? stampPrice : meteredPrice;
// Calculate ounces (round up to next whole ounce is NOT required for extra ounce logic usually,
// but USPS pricing steps are per ounce or fraction thereof).
// Example: 1.1 oz costs same as 2.0 oz.
var chargedWeight = Math.ceil(weight);
var extraOunces = (chargedWeight > 1) ? (chargedWeight – 1) : 0;
totalCost = base + (extraOunces * additionalOzLetter);
details = "Base Rate (1 oz): $" + base.toFixed(2) + "" +
"Additional Ounces: " + extraOunces + " x $" + additionalOzLetter.toFixed(2);
} else if (type === "flat") {
// Flat Constraints
if (weight > 13) {
errorMsg.innerHTML = "Large Envelopes (Flats) cannot exceed 13 oz. Please select 'First Class Package'.";
errorMsg.style.display = "block";
return;
}
var chargedWeight = Math.ceil(weight);
var extraOunces = (chargedWeight > 1) ? (chargedWeight – 1) : 0;
totalCost = flatBasePrice + (extraOunces * additionalOzFlat);
details = "Base Rate (1 oz): $" + flatBasePrice.toFixed(2) + "" +
"Additional Ounces: " + extraOunces + " x $" + additionalOzFlat.toFixed(2);
} else if (type === "parcel") {
// Package Constraints
if (weight > 13) {
errorMsg.innerHTML = "First Class Package (Retail) limit is 13 oz. Heavier items ship via Priority Mail or Ground Advantage.";
errorMsg.style.display = "block";
return;
}
// Approximate Retail Ground Advantage / First Class Package Logic
// Based on weight tiers: 4oz, 8oz, 12oz, 13oz + Zone Multipliers
// This is a simplified estimation matrix.
var weightTier = 0;
if (weight <= 4) weightTier = 1;
else if (weight <= 8) weightTier = 2;
else if (weight <= 12) weightTier = 3;
else weightTier = 4; // up to 13oz
// Base prices array [0, tier1, tier2, tier3, tier4]
// Zone 1/2 base approximate
var baseTierPrices = [0, 5.00, 5.70, 6.50, 7.85];
// Zone Surcharges (simplified for estimation)
// Zone 1/2: +0
// Zone 3: +0.25
// Zone 4: +0.50
// Zone 5: +0.80
// Zone 6: +1.00
// Zone 7: +1.20
// Zone 8: +1.40
// Zone 9: +2.50
var zoneSurcharge = 0;
switch(zone) {
case 1: case 2: zoneSurcharge = 0; break;
case 3: zoneSurcharge = 0.25; break;
case 4: zoneSurcharge = 0.50; break;
case 5: zoneSurcharge = 0.80; break;
case 6: zoneSurcharge = 1.00; break;
case 7: zoneSurcharge = 1.20; break;
case 8: zoneSurcharge = 1.40; break;
case 9: zoneSurcharge = 2.50; break;
}
totalCost = baseTierPrices[weightTier] + zoneSurcharge;
details = "Package Tier: " + ((weightTier-1)*4 + 1) + "-" + (weightTier*4 < 13 ? weightTier*4 : 13) + " oz" +
"Zone " + zone + " Estimate";
}
// Display Result
costDisplay.innerHTML = "$" + totalCost.toFixed(2);
breakdownDisplay.innerHTML = details;
resultBox.style.display = "block";
}
Understanding First-Class Mail Rates
USPS First-Class Mail® is the most popular and affordable way to send envelopes and lightweight packages. Whether you are sending a personal letter, a bill, or a small product sold online, understanding how the rates are calculated is essential for proper budgeting.
Types of First-Class Mail
The cost of your postage depends largely on the physical characteristics of your mailpiece:
Letters: Standard envelopes. Must be rectangular and machinable. Max weight is 3.5 oz.
Large Envelopes (Flats): Larger than a standard letter (e.g., 9×12 inch envelopes). Must be flexible and uniformly thick. Max weight is 13 oz.
First-Class Package Service (Retail): Small boxes or thick envelopes containing merchandise. Max weight is 13 oz for retail customers. Note: USPS has recently integrated this into "USPS Ground Advantage™", but the pricing tier remains similar for light items.
Current Pricing Breakdown (2024/2025 Estimates)
Mail Type
Starting Price (1 oz)
Additional Ounce Price
Maximum Weight
Standard Letter
$0.73
$0.24
3.5 oz
Metered Letter
$0.69
$0.24
3.5 oz
Large Envelope (Flat)
$1.50
$0.24
13 oz
Zone-Based Pricing for Packages
While letters and flats have a fixed "flat rate" across the country regardless of distance, First-Class Packages are priced based on the distance they travel. USPS divides the US into "Zones" ranging from Zone 1 (local) to Zone 9 (farthest territories).
This calculator estimates package costs by combining weight tiers (e.g., 1-4 oz, 5-8 oz) with destination zones. The farther the destination, the higher the postage cost for parcels.
How to Avoid Returned Mail
Weigh Correctly: Always round up to the next ounce. If your letter weighs 1.1 oz, you must pay the 2 oz rate.
Check Dimensions: A letter that is rigid, square, or has clasps may be subject to a "non-machinable surcharge" (approx. $0.44 extra).
Use the Right Service: If your envelope weighs more than 13 oz, it must be upgraded to Priority Mail.