The quick answer
Bulgur is cracked wheat that has been precooked and dried. Couscous consists of small granules usually made from wheat semolina. They can serve similar roles, but their preparation and texture differ. Check the exact product before swapping.
In this guide
Read the product name
Fine and coarse bulgur are not identical. Standard couscous and pearl couscous also need different methods. Do not treat a soaking instruction for instant couscous as suitable for every product.
Decide what the dish needs
For a loose side dish, either may work with a suitable method. In a stuffed vegetable or formed mixture, texture and absorption help hold the dish together. A substitution can change the structure, not just the flavor.
Cook each product correctly
Follow the package or a recipe written for that grain size. Do not carry over the water quantity and cooking time unchanged. For a cold salad, cook and cool the grain appropriately before adding delicate herbs.
Check allergens and the final portion
Wheat bulgur and wheat couscous contain gluten. A rice- or corn-based product is a separate ingredient, not evidence that ordinary couscous is gluten-free. Weigh the finished portion if the recipe specifies cooked weight; nutrition estimates change when ingredients change.
A few useful answers
Can I replace bulgur with couscous in tabbouleh?
You can make a variation, but the texture and grain preparation will differ.
Is pearl couscous the same as fine couscous?
No. Use the instructions for the specific product.
Sources and further reading
Use the full recipe alongside these tips, and follow the stated care and safety limits of your equipment.