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Sizing Up Your Mail

Although the season to be jolly is well and truly over some things are always certain at the turn of every New Year; tax returns are due, that new gym membership form won’t send itself and you’re definitely going to return those clogs your wacky Aunt Barb bought you for Xmas. This means you’re going to need to send packages and the last thing you need is to have them held at the Post Office because you’ve got your mailbag size wrong. We know in January you are still playing catch up from the festive break, so we’ve created a handy formula to tell help you size up which mail bag you need!

When measuring your goods please remember to use an accurate tool such as a tape measure to measure the length, width and diameter of your goods, either boxed or as though it is in an imaginary box. Please note the formula works out the minimum measurements required for length and width.

So take those clogs from Aunt Barb, of course they’re comically big so you’re going to need an even bigger box and an even bigger mail bag.  Let’s say these are your measurements:

(L)      12”      305mm

(W)      9”      230mm

(D)      5”       125mm

The minimum width= W+D+1” so in the clogs case this would be 9”+5”+1”= 15”. Therefore the minimum width of your mail bag should be 15”.

The minimum length =L+D+1” so in this case it would be: 12”+5”+1”=18”. Therefore the minimum length of your mail bag should be 18”.

So to get those clogs sent to Timbuktu we would advise a 16” x21” mailing bag. This can be found here.

The formula is also accurate in metric measurements if you take into account 25.4mm=1” so using the clogs as an example minimum width= 230+125+15.4=380.4mm. Therefore minimum width of your mailing bag should be 380.4mm

To find the length 305+125+25.4=455.4mm. Therefore minimum length of your mailing bag should be 455.4mm.

This again would equate to the same bag but in metric is 400mm x 525mm (which is the equivalent to a 16” x 21” mailing bag)

Remember when sending any packages you should use the Royal Mail sizing guide to work out which category your package falls into, so that its journey is as hassle free as possible. We have created a table of these categories for you to reference when ordering mail bags from ODL packaging.


Type of package Max Weight Max length Max width Max diameter Our recommended products
Letter 100g 24cm/9.5” 16.5cm/6.5” 5mm/ 0.5” Commercial envelopes
Large Letter 750g 35.3cm/13.5” 25cm/10” 2.5cm/1” Large Letter Wraps
Small Package 2kg 45cm/ 18” 35cm/13.5” 16cm/6.5” Small cardboard boxes
Large package 20kg 61cm/24” 46cm/18.5” 46cm/18.5” Large cardboard boxes