Where to buy citric acid
Everyone sells it and almost nobody sells it in the size or the grade you want. Here is where to look and what to check before you order.
Buy citric acid from a soap supplier or a brewing shop rather than the baking aisle — the same product in a 100 g tub costs several times as much per kilo. Ask for anhydrous, fine granule, food grade if it is offered. A 1 kg bag makes roughly 26 standard bath bombs, which is the right first order for most people.
Citric acid is not restricted, not dangerous and not rare. It is simply sold, almost everywhere, in the wrong size. The baking aisle has it in 100 g tubs meant for jam-making, the cleaning aisle has it mixed with things you do not want in a bath, and the industrial suppliers have it in 25 kg sacks. Finding the middle is the entire problem, and it is why this question gets asked as often as it does.
The scale is worth knowing before you order. A standard 65 mm bath bomb takes about 151 g of mix, of which roughly 38 g is citric acid — so a kilo is about 26 bombs. Anyone making bath bombs for presents wants a kilo. Anyone selling them wants five, and a plan for keeping it dry.
Two things matter more than where you buy it: the granule size and whether it is anhydrous. Both are covered below. If you cannot get it at all, the substitutes guide is honest about how much worse the alternatives are — and the honest answer for most people is to solve the sourcing rather than change the recipe.
Where to look
Ranked by how well each actually serves someone making bath bombs at home. We do not name shops or quote prices — stock and terms change constantly, and a stale recommendation is worse than none.
How much to order
Enough to find out whether you enjoy this. It will be gone in two evenings if you do.
The right first real order. Big enough to be worth the postage, small enough to use before the bag has been open long enough to matter.
Only once you are selling. Opened citric acid pulls water out of the air and sets into a block, so buying ahead has a real cost.
What to check before you order
Monohydrate citric acid carries a water molecule, which makes it heavier per acidic proton — about 91% of the fizz of anhydrous, gram for gram, so you need roughly 9% more of it for the same result. Worse, that bound water is why it cakes faster in a damp cupboard. Most craft suppliers sell anhydrous by default; it is worth confirming.
Coarse crystals sit in the mix like grit, and a bath bomb packed around them has weak points running through it — those are the seams it breaks along. Fine granule packs tighter, binds better and gives a smoother finish. If all you can get is coarse, a few seconds in a spice grinder fixes it, with a mask on.
Bath bombs are not eaten, so what "food grade" buys you here is mostly a guarantee that nothing else is in the bag. A technical grade from a reputable supplier that states its purity is the same chemical. What you are actually avoiding is an unlabelled cleaning product with a surfactant in it.
Citric acid is hygroscopic — it draws water from the air, and a caked bag is a bag that has already started to react at its surface. Buying 132 bombs' worth to save on postage is a false economy if it takes you two years and turns into a brick in month four. Decant into sealed jars if you do buy big.
Citric acid is a third of the fizz base by weight and the first thing you run out of — 226 g in a single 6-bomb batch against 453 g of bicarbonate, which you can buy anywhere in any quantity. Plan your orders around the citric acid and the bicarbonate looks after itself.
Buying well
The baking aisle is not expensive because of the acid, it is expensive because of the tub. Work every listing back to a price per kilo before comparing, including the postage, and the ranking changes completely.
Bicarbonate of soda is a supermarket product sold in kilos for very little, and paying craft-supplier prices for it is the commonest way to make a batch cost more than it should. The two ingredients do not have to arrive in the same box.
A fold-over bag gains weight in a kitchen. A screw-top tub or a bag you decant into jars keeps the acid accurate for years, which matters because every batch you weigh from it afterwards inherits the error.
Several cleaning products are largely citric acid. They also routinely contain surfactants, chelators and perfume that are not disclosed on the front of the box, and you cannot calculate a recipe against an unknown — or put one in a bath.
A 6-bomb batch takes 226 g. Run your own mould through the recipe builder and you will know exactly what a bag buys you rather than guessing at it.
Work out what a bag buys you
Enter your mould and how many you want to make, and the recipe builder shows the citric acid the batch takes — so you can order once rather than three times.
Open the recipe builder →Keep the ratio to hand
The bicarb-to-citric ratio, binder rates and mould weights on one printable card. Free.
Estimates, not advice. Every figure on this page is computed from published reference values and standard measures, so your own inputs, equipment and conditions will move it. Nothing here is professional advice — talk to a qualified professional before acting on it.