STOCKHOLM—IKEA, the Swedish furniture giant, expects to increase revenue as much as 85% by 2020, as well as more than double the number of people who walk through its doors on an annual basis. IKEA said it plans to generate between €45 billion and €50 billion ($58.8 billion to $65.3 billion) in annual revenue, up from an estimated €26.9 billion in the most recent fiscal year ended Aug. 31.