I adore recipes written in grams, its so much easier to duplicate results time after time! I've been using and loving this volume-weight chart for awhile and it recently occurred to me to test its accuracy. I scooped the flours out of the bags with my measuring scoop and then leveled it off. I was stunned by how much variation there was from the chart.
Amaranth: 140g instead of 120g
Brown Rice: 148g instead of 158g
Cornmeal:150g instead of 128g
Millet: 172g instead of 120g
Oat flour: 88g instead of 120g
Pea protein powder: 144g (split pea flour is 160g)
Sorghum: 156g instead 127g
Sweet rice: 180g instead of 204g
Tapioca: 140g instead of 125g
Brown teff: 152g instead of 120g
(an average difference of about 30g per cup of flour from the standard!)
1) Measuring 101: When a recipe calls for 1 cup of brown rice flour, it is asking for 158g. The proper way to measure flour is to sift first or spoon it out of the bag into the cup. (Don't scoop it out of the bag with your cup or tap the cup after you fill it like me.) Then level the flour with a straight edge. Even if you do this, you probably won't get exactly 158 grams, just something close. Volumetric measurement is really imprecise. It works for general cooking, but for baking mass is better.
2) Your flour may my be too fine or too coarse making it more or less dense than typical. I grind my own flour and it is superfine.
4) You don’t know the accuracy of the cups or flour texture the author of your recipe used, you can only guess based on their level of expertise as a baker. A less expert baker probably scooped their flour with the cup and will have higher flour weights per cup, around 25g. If you convert to mass you may be off by as much as 50g! If you're not sure about the recipe author's measuring technique, use cups and do not convert to grams using a chart.
5) If you add 1/4 cup of four types of flour like we often do in gluten free baking, you have four chances to add slightly too much or slightly too little flour, you won’t notice like you would with 1 cup of one type of flour. You could be off by as much as 1/4 cup of flour per cup in the end even if your flour was nicely sifted!
What to do:
1) Look for recipes written in grams!
2) Use measuring cups if the recipe is written in cups and developed by a regular person at home it is probably closer than the weight conversion. Also, they most likely scooped their flour out of the container rather than spoon filling or sifting their flour, so do it that way.
3) Ask the recipe author about how they measure their flour and if their flour is a standard storebought flour (Bob's, King Arthur, etc), home ground, superfine, gritty, etc. If they have superfine home ground flour instead of storebought flour, their flour might be denser per cup by 10-20g.
3) Expect that recipes from professionals will be the most likely to convert well from volume to weight because they measure more accurately and often use store bought flours.
4) If adding small amounts of lots of different flours, be extra careful to make sure each flour addition is measured accurately. Look for recipes that have you blend the flour separately and then add one measurement of the blend, there is much less room for error.