This is the question we get asked most, and it is worth two minutes of your time, because a lid that is slightly the wrong size is one of the main reasons a jar refuses to seal.
There are only two sizes
Almost every mason jar you will find in Australia is one of two openings:
- Regular mouth, 70mm (about 2.76 inches). The narrower neck. Classic jam jar shape, tapers in at the shoulder.
- Wide mouth, 86mm (about 3.39 inches). Straight sides all the way up, no taper.
That is it. Jar height and volume vary, but the opening is nearly always one of those two.
How to tell in ten seconds
Look at the shoulder. If the jar narrows near the top before it reaches the thread, it is regular mouth. If the sides run straight up to the rim, it is wide mouth. This works for most jars without measuring anything.
Or measure it. Put a ruler across the opening, inside edge to inside edge. Roughly 70mm means regular. Roughly 86mm means wide.
Or use your hand. If you can get your whole hand into the jar comfortably, it is wide mouth. If you are fishing around with two fingers, it is regular.
Which should you buy?
Wide mouth is easier to live with. Easier to fill, easier to scoop out of, easier to wash. If you are buying jars from scratch and have no strong preference, go wide.
Regular mouth suits smaller portions. Spices, herbs, coffee for a week, anything you decant rather than dig into. The narrower opening also means slightly less air to pull out.
Most people end up with some of each, which is fine. Our glass mason jars come in both, in 500ml and 750ml, sold in 4-packs.
The bit that actually matters: matching lids
The sealing lid has to sit flat and flush on the rim. Not overhanging the edge, not rattling around inside it.
A lid that is slightly too large will look like it fits, will sit at a barely visible angle, and will not hold a vacuum. If a jar keeps failing to seal and you are sure the rim is dry, check the lid size first.
So: small lid for regular-mouth 70mm jars, large lid for wide-mouth 86mm jars. Our metal sealing lids and chalkboard lids both come in each size, in packs of 12, 24 or 36.
What about the sealer itself?
One sealer handles both. The FoodVault jar sealer works on regular and wide-mouth jars, and on most jars of a similar diameter, so you do not need a different machine for each. You only need the right lid.
And the funnels
Same logic. Our stainless steel funnel set includes both sizes, which saves a lot of spilled rice on the bench.
Ready to seal something? Here is how to use your jar sealer, step by step.