Postcard
Letter (Standard)
Letter (Metered)
Large Envelope (Flat)
Base Rate (1 oz):$0.00
Additional Ounces (0 x $0.00):$0.00
Non-Machinable Surcharge:$0.00
Total Postage:$0.00
function updateOptions() {
var type = document.getElementById('mailType').value;
var surchargeDiv = document.getElementById('surchargeContainer');
var weightInput = document.getElementById('weightAmount');
// Postcards have fixed dimensions/weight constraints generally, usually treated as 1 unit
// Flats don't typically have the "Non-machinable" surcharge in the same way letters do (though they have rigidity rules).
// For simplicity, we hide non-machinable for flats and postcards in this UI logic, or leave it for letters.
if (type === 'letter_std' || type === 'letter_metered') {
surchargeDiv.style.display = 'flex';
} else {
surchargeDiv.style.display = 'none';
document.getElementById('nonMachinable').checked = false;
}
}
function calculatePostage() {
// — 1. Get Inputs —
var mailType = document.getElementById('mailType').value;
var weightInput = document.getElementById('weightAmount').value;
var isNonMachinable = document.getElementById('nonMachinable').checked;
var errorDisplay = document.getElementById('errorDisplay');
var resultBox = document.getElementById('resultBox');
// — 2. Reset Display —
errorDisplay.style.display = 'none';
errorDisplay.innerHTML = ";
resultBox.style.display = 'none';
// — 3. Validate Weight —
var weight = parseFloat(weightInput);
if (isNaN(weight) || weight 1 oz (rare for card stock), warn them.
// We will just apply the fixed rate but note it.
chargedWeight = 1; // It's a single unit price.
}
// Check Max Weight Limits
if (mailType === 'letter_std' || mailType === 'letter_metered') {
if (weight > 3.5) {
limitExceeded = true;
limitMsg = "Letters weighing over 3.5 oz must be mailed as Large Envelopes (Flats). Please change the Mail Type.";
}
} else if (mailType === 'flat') {
if (weight > 13) {
limitExceeded = true;
limitMsg = "First Class Mail Large Envelopes cannot exceed 13 oz. Items over 13 oz must be shipped via USPS Ground Advantage or Priority Mail.";
}
}
if (limitExceeded) {
errorDisplay.innerHTML = limitMsg;
errorDisplay.style.display = 'block';
return;
}
// — 6. Calculate Cost —
var totalCost = 0;
var extraOz = 0;
var extraCost = 0;
var surchargeCost = 0;
if (mailType === 'postcard') {
totalCost = baseRate;
extraOz = 0;
} else {
// First ounce is covered by baseRate.
// Remaining ounces: chargedWeight – 1
if (chargedWeight > 1) {
extraOz = chargedWeight – 1;
extraCost = extraOz * addOzRate;
}
totalCost = baseRate + extraCost;
if (isNonMachinable && (mailType === 'letter_std' || mailType === 'letter_metered')) {
surchargeCost = surcharge;
totalCost += surchargeCost;
}
}
// — 7. Display Results —
document.getElementById('baseWeightDisplay').innerText = "1";
document.getElementById('baseCostDisplay').innerText = "$" + baseRate.toFixed(2);
document.getElementById('extraOzCount').innerText = extraOz;
document.getElementById('extraOzRate').innerText = addOzRate.toFixed(2);
document.getElementById('extraCostDisplay').innerText = "$" + extraCost.toFixed(2);
// Toggle Rows based on relevance
if (extraOz > 0) {
document.getElementById('additionalOzRow').style.display = 'flex';
} else {
document.getElementById('additionalOzRow').style.display = 'none';
}
if (surchargeCost > 0) {
document.getElementById('surchargeRow').style.display = 'flex';
document.getElementById('surchargeCostDisplay').innerText = "$" + surchargeCost.toFixed(2);
} else {
document.getElementById('surchargeRow').style.display = 'none';
}
document.getElementById('totalCostDisplay').innerText = "$" + totalCost.toFixed(2);
resultBox.style.display = 'block';
}
Understanding USPS First Class Mail Rates
Postage rates can be confusing, with different prices for standard letters, metered mail, and large envelopes. This USPS First Class Mail Rate Calculator helps you determine the exact postage required for your domestic mail based on the current weight-based pricing structure.
How to Use This Calculator
Select Mail Type: Choose between a Postcard, Standard Letter (stamped), Metered Letter (business postage meter), or Large Envelope (Flat).
Enter Weight: Weigh your item in ounces. A standard kitchen scale is usually sufficient for this.
Check Surcharges: If your letter is square, rigid, or has an uneven surface (like a wax seal or clasp), check the "Non-Machinable" box.
Calculate: Click the button to see the total postage cost broken down by base rate and additional ounces.
Weight Limits and Rules
Mail Type
Max Weight
Base Rate (1 oz)
Add'l Ounce Rate
Postcard
N/A (Dimensions apply)
$0.53
N/A
Letter (Standard)
3.5 oz
$0.68
$0.24
Letter (Metered)
3.5 oz
$0.64
$0.24
Large Envelope (Flat)
13 oz
$1.39
$0.24
Common Questions
What counts as a "Large Envelope" (Flat)?
To qualify as a flat, your mailpiece must exceed the dimensions of a standard letter (11-1/2″ long x 6-1/8″ high) but remain under 15″ long x 12″ high x 3/4″ thick. It must also be flexible. If it is rigid, it may be classified as a package (Ground Advantage), which costs significantly more.
What is the Non-Machinable Surcharge?
Standard letters pass through high-speed sorting machines. If a letter is square, rigid, has clasps/strings/buttons, or the address is parallel to the shorter edge, it cannot be machined. USPS charges an extra fee (currently approx. $0.44) to process these items manually.
What happens if my letter is over 3.5 ounces?
If a standard letter weighs more than 3.5 ounces, it no longer qualifies for the Letter rate. It is automatically categorized as a Large Envelope (Flat), and you must pay the Large Envelope price starting at the 1 oz rate ($1.39) plus additional ounces.