Ran out of tomato paste mid-recipe? Ketchup will do the job at 1 tbsp tomato paste + 1 tbsp water + 1 tsp sugar per 2 tbsp ketchup — but only if you also adjust for what the swap takes away or adds. Condiments and tomato products swap by concentration and flavour, not just by volume. A paste is far more concentrated than a sauce, a sweetened ketchup is a different ingredient from an unsweetened paste, and two brown sauces that look alike on the spoon can taste nothing alike in the pan. This page gives the ratio, shows it in a table for the amounts you will actually meet, and walks through three real dishes so you can see where the swap works and where it changes the dish into something else.
The ratio, in a table
The table below converts tomato paste to ketchup for the amounts you are most likely to meet. The rule is always the same: 1 tbsp tomato paste + 1 tbsp water + 1 tsp sugar per 2 tbsp ketchup.
| Tomato paste called for | Ketchup to use |
|---|---|
| 2 tbsp | 1 tbsp paste + 1 tbsp water + 1 tsp sugar |
| 1/4 cup | 2 tbsp paste + 2 tbsp water + 2 tsp sugar |
| 1/3 cup | 2 tbsp + 2 tsp paste + 2 tbsp + 2 tsp water + 2 tsp + 2/3 tsp sugar |
| 1/2 cup | 1/4 cup paste + 1/4 cup water + 1 tbsp + 1 tsp sugar |
By weight, one cup of tomato paste is about 262 g (spooned and levelled, USDA) and one cup of ketchup is about 240 g (spooned and levelled, USDA). The two weigh very differently per cup, so measure this swap by volume, not by weight, unless you are converting the whole recipe to grams — and then use the numbers above. All weights on this page are approximate; verify with a kitchen scale when the result matters.
Worked examples
Example 1: Quick pasta sauce
A recipe for a pasta sauce calls for 1 tbsp of tomato paste. Using the ratio, that becomes 2 tbsp of ketchup. Simmer the sauce for a few minutes so the ketchup's sweetness mellows, and taste before adding any more sugar. The sauce will be a touch sweeter than the original, but it will work.
Example 2: Chilli con carne
A recipe for chilli calls for 2 tbsp of tomato paste. Using the ratio, that becomes 1/4 cup of ketchup. Add the ketchup with the tomatoes and let the chilli simmer so the sweetness cooks down. Hold back any sugar the recipe asks for until you have tasted the finished chilli — the ketchup has already added it.
Example 3: Meatloaf mix
A recipe for a meatloaf mix calls for 1 tbsp of tomato paste for depth. Using the ratio, that becomes 2 tbsp of ketchup. Mix it into the meat with the egg and crumbs. The meatloaf will be a little sweeter and a little moister than the original, which suits a meatloaf well.
What changes in the result
Ketchup in place of tomato paste is sweeter, thinner and more vinegary, and the swap needs three adjustments, not one. Tomato paste is concentrated cooked tomato with no added sugar; ketchup is a sweet, thin sauce, so using it straight will make the dish sweeter, thinner and sharper than the recipe intends. The ratio is one tablespoon of paste plus one tablespoon of water plus one teaspoon of sugar per two tablespoons of ketchup — which is a way of saying that ketchup is roughly half paste, half water, with sugar and vinegar added. The result is a sauce that is close to the original in body, but sweeter, so taste before you add any more sugar.
When not to substitute
Do not make this swap where the concentrated depth of tomato paste is the point of the dish. A slow-cooked ragù, a braise, or a stew that depends on paste for its deep, savoury base will be thinner and sweeter with ketchup, and the difference will show. Do not use ketchup in a dish where the sweetness would clash either — a sharp, savoury sauce with capers or olives will taste wrong with ketchup's sugar. And do not use it in a recipe that fries the paste in oil first: ketchup's water and sugar will spit and burn in hot oil, where paste fries cleanly.
Practical guidance
Taste as you go, and add the substitute in stages rather than all at once — it is easy to add more of a salty, sweet or sharp condiment and impossible to take it out. When a recipe calls for a concentrated tomato product, fry the substitute in a little oil for a minute before adding liquid: cooking it briefly deepens the flavour and takes off any raw edge. Balance a sweet swap with a splash of vinegar or lemon juice, and balance a sharp swap with a pinch of sugar. Keep opened jars and bottles in the fridge, label them with the opening date, and freeze leftover tomato paste in tablespoon-sized portions so you never have to open a new tube for a single spoonful. All amounts on this page are approximate; a kitchen scale is the most reliable way to measure sticky pastes and sauces for a large batch.
Frequently asked questions
How much ketchup do I use instead of 1 tbsp of tomato paste?
Use 2 tbsp — the ratio is 1 tbsp of tomato paste plus 1 tbsp of water plus 1 tsp of sugar per 2 tbsp of ketchup. In practice, that means 2 tbsp of ketchup replaces 1 tbsp of paste, and you should hold back any sugar the recipe asks for.
Will the dish be sweeter?
Yes — ketchup is sweetened, and tomato paste is not. Taste the finished dish before adding any more sugar, and add a splash of vinegar or lemon juice if the sweetness needs balancing.
Can I fry ketchup like tomato paste?
No — ketchup's water and sugar will spit and burn in hot oil, where paste fries cleanly. Add ketchup with the liquid ingredients instead, and let it simmer so the sweetness mellows.
Can I use ketchup in a ragù?
Not as a straight swap. A slow-cooked ragù depends on tomato paste for its deep, savoury base, and ketchup will make it thinner and sweeter. Use ketchup for a quick sauce, and keep paste for a long, slow cook.
Do I need to add water?
The ratio already accounts for it: ketchup is roughly half paste and half water, so 2 tbsp of ketchup replaces 1 tbsp of paste plus 1 tbsp of water. If the sauce looks too thick, add a splash more water; if it looks too thin, simmer it a little longer.
Scaling the swap up or down
A condiment swap scales linearly in the table, but salty, sweet and sharp ingredients do not scale perfectly in the mouth — a doubled recipe often needs slightly less than double the salty or sharp ingredient, because the flavour concentrates as the dish reduces. The safe way to scale up is to add three-quarters of the scaled amount, taste, and then add the rest a little at a time. The same goes for scaling down: a single serving needs the full ratio, but a small error matters more, so measure with measuring spoons rather than by eye. When a recipe is scaled up for a crowd, make the sauce or the dressing in a separate bowl and add it to the main dish gradually, tasting as you go — it is easy to add more of a salty or sweet condiment and impossible to take it out. All amounts on this page are approximate; a kitchen scale is the most reliable way to measure sticky pastes and sauces for a large batch.
If the swap goes wrong — and how to store the substitute
If a tomato sauce tastes tinny or raw, the paste or purée was not cooked long enough — fry it in a little oil for a minute before adding liquid, and the flavour will deepen. If a dressing separates, the mustard or the paste was not whisked in properly: whisk the thick ingredient into the vinegar first, then add the oil in a slow stream while whisking. If a marinade is too sharp, add a pinch of sugar and let the meat marinate for less time next time. Store opened condiments in the fridge and check them before use — a sauce that smells off or has mould on the surface should be thrown away, not scraped clean.