How much does a dL of flour weigh?

There can be no exact general conversion because flour's density depends on how it has packed into a space and also a little on the specific flour – this is why mass measurements are preferred for most serious purposes.

However, there are plenty of resources that will give you a suitable answer and any recipe using volume measurements for solids shouldn't be too dependent on small variations: the first one that came up for me when I googled 'dl flour in grams' was this which gives 52.1g. (The implied level of precision here is misleading of course.)

Building off what @dbmag9 said:

According to Pastries like a pro

• 1 Cup Sifted Flour ~114g, so 1 dL is about 48g.
• 1 Cup Unsifted Flour ~140g, so 1dL is about 59g.

So, if it is "Sifted Flour" or "Flour, Sifted", you would have different weights.

I also looked at King Arthur Baking for "flour".

• Averaging the Wheat flours came out to about 50.55g / 1dL.
• All Purpose flour came out to 50.7g / dL.
• Averaging all 48 types of "flour" listed came out to 47.18g/dL.

dL (deciliter = 0.10 liter [100ml] = 100g of water)

'dL' is used in Sweden as a measuring spoon/cup and 60g is quoted for flour.

Translated from Umrechnung dl = g page listed below:

For those who are not in Sweden, IKEA seems to offer such spoons/cups:

VARDAGEN:

• 1 ml (1 pinch)
• 1 Teaspoon. (5ml)
• 1 Tablespoon (15ml)
• 1/2 Deciliter (50ml)
• 1 Deciliter (100ml) = 0.4226752838 Cup (US)
  • 1 Cup (US) = 2.365882365 dL = 236.5882365ml of water
    • 100ml=236.5882365*0.4226752838

If you know that your flour is 140g per US Cup:

• 1 dL = 59.1745397282g = 140/2.365882365

Sources:

• Swedish Baking Measurements and Measures
• Umrechnung dl = g (in German)
• tsk, msk und dl: Schwedische Maßeinheiten | TROLLLAND (in German)
• VARDAGEN Küchenmaß 5er-Satz - IKEA Deutschland