Almond flour is usually used as a gluten-free wheat flour alternative. While the fact that it has no gluten is important for those who have celiac disease, this nut flour has many other benefits. Among those benefits are its high fiber content and its nutty taste. If you want to replace it with something that has similar properties, consider one of the almond flour substitutes below.
Your best bet: Coconut flour
Despite the fact that it is made with coconuts rather than almonds, coconut flour has many of the properties you want from almond flour. It is gluten-free in addition to high levels of protein and a lower glycemic index than that of wheat flour. Coconut flour will result in baked goods that are fluffier than those made with almond flour but will not provide the same crunch or nuttiness, though it does have a noticeable coconut flavor. In other words, it may be the ideal substitute if you are making snickerdoodles but not for macaroons.
Coconut flour is also a very dry flour when compared to almond flour. As a result, you will need to increase the amount of eggs and other liquid ingredients to compensate. Failing to do this will result in dry, hard baked goods.
Use about a third as much coconut flour as your recipe requires for almond flour. Depending on what you are making, you may need to increase or decrease the amount from there, but it is a good idea to start with a third to determine how a recipe functions.
A decent second choice: Hazelnut flour
Hazelnuts are best known for flavoring liqueurs like Frangelico and for their use in pralines, but they can be finely ground to make a flour just like almonds. The flavor of hazelnut flour is rich and buttery, making it one of the nut flours that is closest in flavor profile to almond flour. It also works well in all of the same applications. It is gluten-free and has about the same amount of carbohydrates as almond flour. The downside of hazelnut flour is that it is not well known or widely available outside of Latin America and Europe.
You can use hazelnut flour as a 1:1 substitute for almond flour.
In a pinch: Walnut flour
Like the flours above, walnut flour is made simply by grinding up walnuts to get as fine a texture as possible. If you are trying to replace almond flour with another nut flour that will give a similar taste and consistency, walnut flour may be another good option to consider. In addition to being gluten-free, walnut flour is low in carbohydrates and has the same low glycemic index that you get with almond flour. You can use walnuts in place of almond flour in many applications, but it may not be a good idea to replace all of the almond flour with walnut flour alone. The problem is that walnut flour can be bitter if it is not diluted. You should also note that since the skin is left on when milling walnuts, walnut flour has a brown color.
If you are making a recipe that calls for almond flour specifically, use a combination of walnut flour and another nut flour. You can start with a 50/50 mix and use the blend as a 1:1 substitute for almond flour.
Other alternatives
Cassava flour is a good option if you do not need a nut flour to replace almond flour. It can provide very similar results to wheat flour, making it a great option for baked goods.