Heaping Tablespoon to Teaspoons
1 heaping tbsp ≈ 4 to 4.5 tsp
about 40% more than a level tablespoon's exact 3 tsp
A heaping tablespoon is filled above the rim with as much as will stay on the spoon without falling off, rather than swept flat with a knife. That makes it roughly 140% of a level tablespoon: about 4 to 4.5 teaspoons instead of the level 3. It is an approximate measure by its nature. How high the heap sits depends on the ingredient and how you scoop, so unlike a level tablespoon (which is exactly 3 teaspoons), a heaping tablespoon has no single exact teaspoon value. Heaped is simply the British spelling of the same thing; a heaped tablespoon and a heaping tablespoon are identical.
Level, Rounded, Heaping and Scant Tablespoon
Only the level tablespoon has an exact teaspoon equivalent. The others are approximate; the percentages follow America's Test Kitchen and Cook's Illustrated measurement testing and vary with the ingredient.
When Heaping Matters
Coffee and cocoa
Heaping on purpose is normal here. A heaping tablespoon of grounds (about 4 to 4.5 tsp) makes a stronger brew than a level one, and precise volume does not matter.
Flour
Heaping is risky. A heaped tablespoon of flour can hold up to 50% more than a level one, the most common cause of dense, dry bakes. Level flour for baking.
Baking powder and soda
Never heap leaveners. The extra amount changes rise and can leave a metallic taste. Always level, sweeping flat with a knife.
Sugar, spices, loose ingredients
Heaping adds a rough 40% and is fine where a little extra will not break the dish. For anything measured for chemistry, level it.