When requesting quotes for parcel deliveries, two key items of information will be needed for instance parcel size and weight. Along with a parcel's destination, this information will determine both which courier services are available to choose from and how much the parcel delivery will cost.

All couriers impose limits and restrictions on the sizes and weights of parcels that they can deliver. Also, for parcels that are considered to be disproportionately light for their size, couriers will usually apply "volumetric pricing" instead of basing their quote on the parcel's actual weight.

One of the first things that a courier's online quote form will ask for is a parcel's dimensions. Measurements will need to be taken for each of a parcel's length, width and height.

If you're worrying about which part of your parcel counts as which dimension (length, width and/or height), you'll be pleased to hear that it doesn't really matter. It's much more important that you measure the parcel as accurately as possible.

Parcels can be measured easily enough using a standard ruler or tape measure. If you only have a ruler and it's shorter than a side that you're trying to measure, simply measure that side in stages and add the totals.

Couriers normally require customers to measure parcels in cm rather than inches, so be sure to read your figures from the correct side of the ruler or tape measure. With a conversion rate of around 2.5cm to one inch, entering the wrong units could result in overpaying for your parcel delivery as well as a very awkward moment when the courier arrives to collect the parcel.

Couriers set size limits within the specifications that govern what parcels they will accept for delivery. Parcel size limits can include one, two or all three of the following:

- A maximum length for any one side of a parcel (eg no side must measure over, say, 150cm);

- Limits for all three sides (eg maximum parcel dimensions of, say, 120 x 80 x 80cm);

- A maximum overall volume for a parcel (eg 0.23 cubic metres).

Volume is a measure of how much room a parcel takes up and is calculated by multiplying together each of the three dimension measurements (length x width x height). To work out a parcel's volume in cubic metres (the unit most commonly used for specifying volume limits), the dimensions must be converted into metres before being multiplied together.

In certain circumstances, the relationship between a parcel's weight and volume can lead to couriers applying a different approach to pricing the delivery. Where a parcel takes up more space that the weight alone would suggest, many couriers use dimensional or volumetric pricing. This works out a theoretical weight that more fairly (in their view) reflects what the sender should pay considering the amount of space that their parcel will take up. This does make reasonable sense, as a large and yet very lightweight parcel would otherwise cost very little to send, whilst actually taking up quite a lot of space in the courier's vans and/or aircraft.

Couriers therefore use the higher of volumetric weight and actual weight.