The size of your gaiwan or teapot matters a lot, even more than the gaiwan versus teapot decision itself.
In fact, the water volume capacity of your brewing vessel is arguably the single most important factor as you shop for teaware. The choice comes down to how you're brewing tea and whether you plan to drink solo or share with others.
100 ml Gaiwans and Teapots for Solo Sessions and Sharing
For gongfu style tea sessions, 100 ml (3.5 oz) is a good middle ground for both gaiwan size and teapot size. It's not overwhelming for solo sessions but has enough volume to share with two or three other people.
This is where most people should start for their first brewing vessel. It doesn't have to be exactly 100 ml. Any gaiwan or teapot in the 90-120 ml range will be fine for most tea sessions that don't involve large groups. You'll use 6-8 grams of tea for gongfu sessions with these vessels.
30 ml to 80 ml Gaiwans and Teapots for Sampling or Conserving Tea
Now we're talking about a size range that includes smaller gaiwans and miniscule teapots, all the way down to 30 ml (1 oz) capacity. They're cute and fun but some weird things start to happen with very small vessels, which you need to know about.
With an 80 ml (2.7 oz) gaiwan the normal guidelines still apply. You use about 5 to 5.5 grams of tea and steep as usual. This is a good choice if you're more sensitive to tea or find 100 ml sessions tough to finish by yourself.
Going to 70 ml and below, there might be enough tea to share with one other person, but only a small taste. The lower volume of hot water also means the tea doesn't stay hot as long. This size range is great for sampling and conserving tea but doesn't extract as evenly due to the heat loss.
One way to adapt to the sharper temperature drop in tiny brewing vessels is to adjust your leaf ratio down and aim for longer infusions. This helps extract more tea goodness and it works well for sampling teas. With small teapots, you can also shower the exterior with boiling water to keep the interior hotter.
Or you can go in the other direction and pack the tiny teapot or gaiwan full of leaves for an ultra-concentrated brew with short infusion times. With Phoenix dancong teas from the Chaozhou region, this technique delivers an explosion of aromas and flavors. The downside is that you'll miss out a bit on later, longer steeps because of the poor heat retention.
150 ml Gaiwans or Teapots for Special Sessions and Sharing
We're discussing gaiwans and teapots in the general range of 150 ml (5 oz), a common enough size you'll encounter. For normal gongfu style anything over 120 ml (4 oz) is usually excessive for daily tea sessions for one person.
A 150 ml vessel uses about 10 grams of tea. This isn't necessarily an overwhelming amount of tea for everyone, but many tea drinkers would prefer to conserve their tea or have a few different, smaller sessions instead of a single big session. On the other hand, it's a great size for sharing with medium groups, or a more intense session for two.
Of course, you can always use less than 10 grams in a 150 ml gaiwan or teapot. You can fill it partway with less hot water and less leaf to achieve typical gongfu ratios. Or you can fill to the top but use a lower leaf ratio and longer infusion times as your preference dictates.
180 ml to 200 ml Gaiwans and Teapots for Lower Ratios and Groups
These big teapots and gaiwans hold in the ballpark of 180 ml to 200 ml (about 6-7 oz), give or take. This vessel size is popular in China for steeping daily drinker teas that do well with lower leaf ratios and longer infusion times, including green teas, white teas and black teas.
Using 5-7 grams of leaves with boiling water in a 180-200 ml vessel, you can steep quality teas 5-10 times. You can also do a perpetual infusion similar to grandpa style tea in a teapot. Simply refill with boiling water as the pot gets below halfway.
It's worth noting that a large gaiwan requires a sharing pitcher (cha hai or gong dao bei) to distribute to guests, while a big teapot can pour directly into their cups.
Alternatively, you can also use a big gaiwan or teapot with typical gongfu ratios. Loaded with 12-15 grams of tea, these big vessels can handily serve 10 guests with 15 ml (a half oz) of strong tea per steep.
250 ml to 300 ml Teapots and Gaiwans for Western Style and Large Group Sharing
Teapots in the 250 ml to 300 ml (8-10 oz) range are not enormous by Western standards. If you're buying a tea gift for someone who steeps with 2-4 grams of tea for several minutes each time, or uses tea bags, this is the size of teapot you'll want to give them.
Good quality teapots don't require baskets, infusers or other add-ons. A slow and steady pouring technique prevents loose leaves from spilling out into cups.
Naturally, these sizes can also work for giant group gongfu sessions with 17-20 grams of leaves. If you can keep 15+ people focused during a gongfu tea session, tag white2tea because we're impressed.
Big caveat with big gaiwans. They can slosh a lot more than smaller gaiwans and they require a big sharing pitcher to serve others. But they're good for grandpa style tea - sipping directly from the gaiwan with just a few grams of leaves.