Packed weight
Weigh the box after it is taped shut, with everything inside — padding, filler and all. A kitchen scale under-reads anything over about 5 lb; a bathroom scale (you, then you holding the box, subtract) covers the rest.
Before you check out
How to estimate shipping cost
A real estimate needs four numbers: what the box weighs packed, its three dimensions, the ZIP codes on both ends, and which service tier you are willing to accept. Skip one and the figure is a guess. Below is the method, plus what the same box actually quoted on two lanes of very different length on 2026-08-28.
Four inputs, no moreLive captured spreadSame box, two lanes
Weight, size, distance, tier
Those four numbers are the whole estimate. Everything else is detail.
The four numbers that set the price
Dimensions, and dimensional weight
Length, width and height of the outer box, each rounded up to the next whole inch. Past a certain size-to-weight ratio, carriers bill a calculated dimensional weight instead of the number on the scale — a light, bulky box can cost like a much heavier one.
Origin and destination
Both ZIP codes together set the zone, and zone is a bigger swing than most people expect for a domestic move — see the live example below.
Service tier
Cheapest ground, a two-day tier or overnight all price the same box very differently. Decide the real deadline before comparing, since working backward from a fast tier makes every estimate look expensive.
The same box, two lanes, captured 2026-08-28
Nothing about the box changed between these two rows — same 14 x 12 x 8 in carton, same 8 lb, same origin ZIP. Only the destination moved.
| Destination | Carrier and service | Price | Quoted transit |
|---|---|---|---|
| Philadelphia, PA 19103 | UPS Ground | $11.35 | 3-4 business days |
| Philadelphia, PA 19103 | USPS Ground Advantage | $11.35 | 6-7 business days |
| Seattle, WA 98101 | USPS Ground Advantage | $22.80 | 6-7 business days |
| Seattle, WA 98101 | UPS Ground | $22.94 | 10-11 business days |
Zone roughly doubled the price on an unchanged box. That is the single biggest reason a shipping estimate made without both ZIP codes is not really an estimate — weight and size set a starting point, and distance decides how far it climbs from there.
The method, step by step
- Pack it first, then weigh it. An estimate from the item alone always runs light — packing materials, void fill and the box itself routinely add a pound or more.
- Measure the outer box, not the item. Round each side up to the next whole inch. A box that is mostly air still pays for the air on a bulky, light shipment.
- Check dimensional weight before trusting the scale number. Multiply length by width by height and divide by the carrier's divisor (most US ground services currently use 139); if that result beats the actual weight, the carrier bills the higher figure. The full formula and current divisors are on our dimensional weight calculator.
- Enter both ZIP codes, not just one. A price without a destination is a shrug. As the table above shows, the same box can price at roughly double once the zone changes.
- Compare service tiers side by side rather than picking a default. The cheapest ground row and the fastest tier are rarely close, but they are sometimes closer than habit assumes — worth a look before defaulting to whichever option loads first.
Estimating shipping cost, in short
What actually determines a shipping cost estimate?
Four inputs: the packed weight, the box dimensions (which can outrank weight through dimensional pricing), the origin and destination ZIP codes together as a zone, and the service tier chosen. Leave any one of them out and a number is a guess rather than an estimate.
How much does distance really change the price?
On the same 8 lb box we quoted on 2026-08-28, USPS Ground Advantage came back at $11.35 to Philadelphia and $22.80 to Seattle from the same origin — roughly double for the longer zone, with nothing else about the box changed.
Can I estimate without a scale or a tape measure?
Roughly, by naming the item and letting a size estimate stand in, but the number will drift the moment the real box goes on a scale. A rough estimate is fine for deciding whether shipping is worth it at all; a number worth acting on needs the real weight and the real box.
Why do two carriers estimate the same box so differently?
Each carrier runs its own formula for when dimensional weight overtakes actual weight, and each draws its own zone boundaries from its own network of hubs. A bulky, light box can price cheaper on one carrier and dearer on another for exactly this reason, which is the whole argument for comparing rather than assuming one carrier's number applies to all three.
Is a same-day quote actually better than a rule of thumb?
Yes, because zone tables and dimensional formulas change by carrier and by season, and a rule of thumb frozen from an old shipment does not update itself. A live quote runs the current formula against the current box, which a memorized number from six months ago cannot do.