Zone 1 & 2 (Local/Close)
Zone 3
Zone 4
Zone 5
Zone 6
Zone 7
Zone 8 (Far)
Zone 9 (Territories)
Calculated Volume:0.00 cu ft
Cubic Tier:Tier 0.1
Estimated Savings vs Retail:—
Estimated Rate: $0.00
*Rates based on estimated Commercial Plus Pricing. Actual postage may vary by provider.
function calculateCubicRate() {
// Clear errors and results
var errorDiv = document.getElementById('errorMessage');
var resultDiv = document.getElementById('resultBox');
errorDiv.style.display = 'none';
resultDiv.style.display = 'none';
// Get Inputs
var L = parseFloat(document.getElementById('pkgLength').value);
var W = parseFloat(document.getElementById('pkgWidth').value);
var H = parseFloat(document.getElementById('pkgHeight').value);
var weight = parseFloat(document.getElementById('pkgWeight').value);
var zone = parseInt(document.getElementById('shipZone').value);
// Validation
if (isNaN(L) || isNaN(W) || isNaN(H) || isNaN(weight)) {
errorDiv.innerHTML = "Please enter valid numbers for dimensions and weight.";
errorDiv.style.display = 'block';
return;
}
// USPS Cubic Rules Check
if (weight > 20) {
errorDiv.innerHTML = "NOT ELIGIBLE: Weight exceeds the 20 lb maximum for Cubic Pricing.";
errorDiv.style.display = 'block';
return;
}
if (L > 18 || W > 18 || H > 18) {
errorDiv.innerHTML = "NOT ELIGIBLE: No single dimension may exceed 18 inches.";
errorDiv.style.display = 'block';
return;
}
// 1. Round down to nearest 0.25 inch (USPS Rule)
// Logic: Floor(Value * 4) / 4
var rL = Math.floor(L * 4) / 4;
var rW = Math.floor(W * 4) / 4;
var rH = Math.floor(H * 4) / 4;
// 2. Calculate Cubic Feet
// Formula: (L x W x H) / 1728
var cubicFeet = (rL * rW * rH) / 1728;
if (cubicFeet > 0.5) {
errorDiv.innerHTML = "NOT ELIGIBLE: Total volume (" + cubicFeet.toFixed(3) + " cu ft) exceeds the 0.50 cu ft limit.";
errorDiv.style.display = 'block';
return;
}
// 3. Determine Tier
var tier = 0;
if (cubicFeet <= 0.10) tier = 0.1;
else if (cubicFeet <= 0.20) tier = 0.2;
else if (cubicFeet <= 0.30) tier = 0.3;
else if (cubicFeet <= 0.40) tier = 0.4;
else if (cubicFeet <= 0.50) tier = 0.5;
// 4. Rate Lookup (Estimated 2024 Commercial Plus Approximation)
// Tiers: 0.1, 0.2, 0.3, 0.4, 0.5
// Zones: 1-9 (Mapped indices 0-8)
// This matrix represents approximate pricing for demo purposes
var rateMatrix = {
"0.1": {1: 8.35, 3: 8.70, 4: 8.95, 5: 9.30, 6: 9.60, 7: 10.00, 8: 10.50, 9: 14.50},
"0.2": {1: 9.20, 3: 9.60, 4: 9.90, 5: 10.40, 6: 11.20, 7: 12.10, 8: 12.90, 9: 18.20},
"0.3": {1: 10.50, 3: 11.10, 4: 11.60, 5: 12.90, 6: 14.80, 7: 16.50, 8: 18.10, 9: 24.50},
"0.4": {1: 11.60, 3: 12.50, 4: 13.50, 5: 15.60, 6: 18.20, 7: 20.90, 8: 23.50, 9: 32.10},
"0.5": {1: 12.50, 3: 13.90, 4: 14.80, 5: 19.50, 6: 22.80, 7: 26.50, 8: 29.80, 9: 41.50}
};
// Zone 1 and 2 are usually same price
var lookupZone = zone;
if (zone === 2) lookupZone = 1;
var price = rateMatrix[tier.toString()][lookupZone];
// Estimate Retail Price for comparison (Weight based – rough estimate 10lbs priority)
// Just for visual "savings" effect
var retailEstimate = price * 1.45;
var savings = retailEstimate – price;
// Display Results
document.getElementById('resVolume').innerText = cubicFeet.toFixed(4) + " cu ft";
document.getElementById('resTier').innerText = "Tier " + tier.toFixed(2);
document.getElementById('resRate').innerText = "$" + price.toFixed(2);
document.getElementById('resSavings').innerText = "$" + savings.toFixed(2) + " (approx)";
resultDiv.style.display = 'block';
}
Understanding USPS Cubic Pricing
USPS Cubic Pricing (Priority Mail Cubic) is a secret weapon for high-volume shippers. Unlike standard Priority Mail, which charges based on weight and distance, Cubic Pricing charges based on the size (volume) of your package and the distance it travels. This is ideal for small, heavy items weighing up to 20 lbs.
How is Cubic Volume Calculated?
The calculation for USPS Cubic Pricing is specific. It does not strictly follow standard geometric volume. Here is the step-by-step process used by our calculator above:
The Formula: Cubic Feet = (Length x Width x Height) / 1728
However, there are important rules applied before the calculation:
Measurement: Measure dimensions to the nearest 0.25 inch. If a dimension falls between quarter inches, round down to the nearest 0.25 inch.
Max Dimension: No single dimension can exceed 18 inches.
Max Volume: The total cubic value cannot exceed 0.50 cubic feet.
The 5 Pricing Tiers
Once the cubic feet are calculated, your package falls into one of five distinct tiers. The price you pay is determined by this tier and your shipping zone.
Tier 0.1: Up to 0.10 cubic feet
Tier 0.2: 0.101 to 0.20 cubic feet
Tier 0.3: 0.201 to 0.30 cubic feet
Tier 0.4: 0.301 to 0.40 cubic feet
Tier 0.5: 0.401 to 0.50 cubic feet
If your package calculates to greater than 0.50 cubic feet, it is not eligible for Cubic Pricing and must be shipped via standard weight-based Priority Mail.
Eligibility Requirements
To qualify for Cubic Pricing, your shipment must meet specific criteria:
Weight Limit: The package must weigh less than 20 lbs.
Service Class: This applies primarily to Priority Mail.
Access: Generally, this pricing is available through "Commercial Plus Pricing" (CPP). You typically access these rates via third-party shipping software (like Pirate Ship, Shippo, or Stamps.com) rather than at the retail Post Office counter.
Why Use a Cubic Rate Calculator?
Using a Cubic Rate Calculator allows you to optimize your packaging. For example, shaving just 0.25 inches off the height of a box could drop you from Tier 0.3 to Tier 0.2, potentially saving dollars per shipment. For e-commerce businesses shipping dense items like books, liquids, paper, or metal goods, switching to cubic pricing is one of the most effective ways to reduce shipping overhead.