Keşke beden tablosunda daha büyük bir beden olsaydı.

Keşke is used to express a wish, usually about something the speaker feels is not true or not available.

In this sentence, it signals a wish like if only... or I wish.... It often introduces a slightly regretful or disappointed feeling.

So the speaker is not just stating a fact; they are wishing the situation were different.

After keşke, Turkish very often uses forms that look like past or conditional forms to express an unreal wish.

olsaydı comes from olmak and is built like this:

• ol- = be / exist / become
• -sa / -se = conditional
• -ydı / -ydi = past form of to be

So olsaydı literally looks something like if it were / if there had been, but after keşke it naturally expresses a wish.

In other words, Turkish uses this kind of form not because the speaker is necessarily talking about the past, but because it marks an unreal or contrary-to-fact wish.

Even though olsaydı looks past, the wish can easily be about the present situation.

That is very common in Turkish:

• Keşke burada olsaydı. = I wish he/she were here.
• Keşke daha ucuz olsaydı. = I wish it were cheaper.

So in your sentence, the speaker is most likely looking at the size chart now and wishing that it included a larger size. The grammar shows an unreal wish, not necessarily a past-time event.

Beden tablosunda breaks down like this:

• beden = size
• tablo = table / chart
• tablosu = its chart / the chart of ...
• tablosunda = in its chart / in the chart

As a noun compound, beden tablosu means size chart.

Then the locative ending -da / -de is added, giving in the size chart.

So:

• beden tablosu = size chart
• beden tablosunda = in the size chart

That -n- is a linking consonant that appears when a case ending is added after a third-person possessive suffix.

Here is the structure:

• tablo
• tablosu = its chart / the chart of ...
• tablosu + -da
• this becomes tablosunda

That -n- helps connect the possessive form to the case ending smoothly.

You will see the same thing in forms like:

• evinde = in his/her house
• arabasında = in his/her car
• kitabında = in his/her book

The two beden words are doing different jobs.

• The first beden is part of the compound beden tablosu = size chart
• The second beden means size as the item the speaker wants

So the sentence is basically saying:

• in the size chart
• there should be a larger size

This repetition may sound a bit redundant in English, but it is perfectly normal in Turkish.

It means a bigger size or a larger size.

Breakdown:

• daha = more
• büyük = big
• daha büyük = bigger / larger
• bir beden = a size

Turkish usually makes comparatives with daha + adjective:

• daha küçük = smaller
• daha pahalı = more expensive
• daha iyi = better

So daha büyük bir beden is literally a more big size, which English expresses as a bigger size.

Here bir works like the English indefinite article a.

So:

• beden = size
• bir beden = a size

It can also still carry its original sense of one, depending on context, but here the natural reading is simply a larger size.

It can mean both, depending on context.

Common meanings include:

• body
• size for clothes

In this sentence, because of beden tablosu and the shopping/clothing context, beden clearly means size.

That is very common in Turkish retail language:

• Hangi beden giyiyorsunuz? = What size do you wear?
• Bedeniniz var mı? = Do you have my size?

Yes, olsa is also possible, and it would still express a wish.

Very roughly:

• Keşke ... olsa = I wish there were ...
• Keşke ... olsaydı = If only there were ... / I wish there were ...

Both are natural, but olsaydı often feels a little more emotionally marked, more explicitly contrary to reality, or a little more reflective. In everyday use, both can work.

So a learner should recognize both as possible with keşke.

Turkish normally places the finite verb at the end of the sentence.

So the structure here is very typical:

• Keşke
• location: beden tablosunda
• thing wished for: daha büyük bir beden
• verb: olsaydı

That final position for the verb is one of the most basic word-order patterns in Turkish.

Yes, Turkish word order is flexible, but the original order is the most neutral and natural here.

For example, you might also hear something like:

• Keşke daha büyük bir beden beden tablosunda olsaydı.

That puts extra emphasis on daha büyük bir beden.

Still, the original sentence sounds smoother and more standard for neutral speech.

Not exactly.

• büyük beden often means plus size as a category
• daha büyük bir beden means a larger size than the ones currently available

So in your sentence, daha büyük bir beden is the better choice because the speaker is wishing for a size larger than the ones listed, not necessarily referring to the general category plus size.