How many cups is 100g of tomato ketchup?

100g of tomato ketchup (ketchup) is

⅓ cup + 1 tbsp

That's 0.42 US cups, 0.39 metric cups, or 6 level tablespoons.

Worked out from 1 US cup = 240g. Cups are rounded to the nearest kitchen fraction, with what's left over in level tablespoons. If you have scales, weighing is more accurate.

Other amounts of tomato ketchup

200g: ¾ cup + 1 tbsp
250g: 1 cup + 1 tbsp
1 cup: 240g
Half a cup: 120g
A quarter cup: 60g
1 tablespoon: 17g
Full table for tomato ketchup

Where these numbers come from

USDA FoodData Central, SR Legacy, food 11935: “Catsup”. USDA lists these household measures for it:

1 tbsp = 17g
1 packet = 9g
1 cup = 240g

Fractions of a cup are the cup weight scaled down. The teaspoon is a third of the tablespoon. Metric-cup figures assume a 250ml cup, and Australian tablespoons hold 20ml. Weights under 10g are rounded to 0.1g, everything else to the nearest gram. Full source list.