Floral Preservative Calculator

Flower food and water for a set of vases, with the water volume worked out from the vase dimensions.

Flower food is dosed by the litre, so the real question is how much water the vases hold. This calculator works the water volume out from the vase diameter, the depth of water and the shape of the vase, multiplies it across the vases you are filling, and returns the water in litres and the preservative in grams at the dose you enter. It also converts the total into sachets, because most flower food is bought and used by the sachet rather than weighed.

At a glance

What you enter: Vase shape, Average inside diameter, Depth of water in the vase, How many vases, Preservative dose, Times the water is changed, Water one sachet is meant for, Weight of one sachet, Price per sachet, Spare allowance for spillage and topping up
What you get: Water one vase holds, Water for all the vases, Water including the spare allowance, Preservative per vase, Preservative for the first fill, Sachets for the first fill, Water over the whole display, Preservative over the whole display, Sachets over the whole display, Cost of the preservative, Preservative cost per vase
Formula shown: Yes, every step, right below your results.
Cost and privacy: Free, no account needed, and nothing you type is stored.

See worked examples ↓ Read the FAQ ↓ Share this calculator ↓

Vase shape

The option value is the share of a straight cylinder the vase really holds. A bulb vase of the same height and width holds far less water.

Average inside diameter cm

Measured across the middle of the water column, not at the rim of a narrow necked vase.

Depth of water in the vase cm

Two thirds full is usual. Some stems stand in shallow water.

How many vases

Preservative dose g per litre

Flower food is dosed at about 5 to 10 g per litre. Use the figure printed on the pack you bought.

Times the water is changed

Fresh water and a fresh dose every day or two. Three changes covers a four to six day event.

Water one sachet is meant for litres

Most sachets make 500 ml to 1 litre. Set to zero if you buy loose powder by weight.

Weight of one sachet g

Used to check the sachet count against the weighed dose.

Price per sachet

Your own figure.

Spare allowance for spillage and topping up %

Reset

Results are estimates for general information only, always verify with a professional or official source before acting on them.

How to use the Floral Preservative Calculator

1 Enter Vase shape, The option value is the share of a straight cylinder the vase really holds. A bulb vase of the same height and width holds far less water.
2 Enter Average inside diameter (cm), Measured across the middle of the water column, not at the rim of a narrow necked vase.
3 Enter Depth of water in the vase (cm), Two thirds full is usual. Some stems stand in shallow water.
4 Enter How many vases
5 Enter Preservative dose (g per litre), Flower food is dosed at about 5 to 10 g per litre. Use the figure printed on the pack you bought.
6 Enter Times the water is changed, Fresh water and a fresh dose every day or two. Three changes covers a four to six day event.
7 Enter Water one sachet is meant for (litres), Most sachets make 500 ml to 1 litre. Set to zero if you buy loose powder by weight.
8 Enter Weight of one sachet (g), Used to check the sachet count against the weighed dose.
9 Enter Price per sachet, Your own figure.
10 Enter Spare allowance for spillage and topping up (%)
11 Press Calculate. You get Water one vase holds, Water for all the vases, Water including the spare allowance, Preservative per vase, Preservative for the first fill, Sachets for the first fill, Water over the whole display, Preservative over the whole display, Sachets over the whole display, Cost of the preservative, Preservative cost per vase, and every intermediate step stays visible under "How is this calculated?"
12 Change one number at a time to see what moves the result, that is usually the most useful thing a calculator can tell you.

Worked examples

Real numbers run through this calculator. Open any example to load it into the form above and change it.

Twenty tapered vases at a wedding

A 12 cm inside diameter, 15 cm of water and a 7 gram per litre dose.

You enter

Vase shape: 0.85
Average inside diameter: 12 cm
Depth of water in the vase: 15 cm
How many vases: 20
Preservative dose: 7 g per litre
Times the water is changed: 3
Water one sachet is meant for: 1 litres
Weight of one sachet: 10 g
Price per sachet: $0.25
Spare allowance for spillage and topping up: 10%

You get

Water one vase holds: 1.44 litres
Water for all the vases: 28.84 litres
Water including the spare allowance: 31.72 litres
Preservative per vase: 10.09 g
Preservative for the first fill: 222.07 g
Sachets for the first fill: 32
Water over the whole display: 95.17 litres
Preservative over the whole display: 666.20 g
Sachets over the whole display: 96
Cost of the preservative: $24.00
Preservative cost per vase: $1.20

About 1.44 litres a vase, so 28.8 litres for the room and 31.7 with the spare allowance: 222 grams of powder, or 32 sachets, for the first fill and 95 sachets across three water changes.

Open this example in the calculator →

Twenty narrow necked bottles

The same height and width, but a bottle shape that holds about a third of the water.

You enter

Vase shape: 0.35
Average inside diameter: 12 cm
Depth of water in the vase: 15 cm
How many vases: 20
Preservative dose: 7 g per litre
Times the water is changed: 3
Water one sachet is meant for: 1 litres
Weight of one sachet: 10 g
Price per sachet: $0.25
Spare allowance for spillage and topping up: 10%

You get

Water one vase holds: 0.59 litres
Water for all the vases: 11.88 litres
Water including the spare allowance: 13.06 litres
Preservative per vase: 4.16 g
Preservative for the first fill: 91.44 g
Sachets for the first fill: 14
Water over the whole display: 39.19 litres
Preservative over the whole display: 274.32 g
Sachets over the whole display: 40
Cost of the preservative: $10.00
Preservative cost per vase: $0.50

About 0.59 litres a vase, so 13 litres across the room and only 91 grams of powder for the first fill. The shape of the vase moves the order by more than the number of vases does.

Open this example in the calculator →

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Frequently asked questions

How much flower food do I put in a vase?

About 5 to 10 grams per litre of water, or one sachet for every 500 ml to 1 litre depending on the brand and the size of the sachet. Use the figure printed on your own pack, because formulations differ. A vase holding 1.4 litres needs roughly 10 grams at 7 grams per litre, which is one sachet made for a litre plus a little more, or a third of a sachet made for 500 ml.

How much water does a vase hold?

Work it out as a cylinder and then correct for the shape: pi times the radius squared times the depth. A vase with a 12 cm inside diameter holding 15 cm of water is about 1700 ml as a cylinder, about 1440 ml in a slightly tapered vase, about 1000 ml in a bulb vase and only about 590 ml in a bottle. Measure across the middle of the water column rather than at the rim, because a narrow neck hides a wide body.

Do I need to change the water and re-dose?

Yes, every day or two, with fresh water and a fresh dose each time. Flowers drink, and the water left behind accumulates bacteria that block the stems and shorten the vase life, which is the opposite of what the preservative is for. Over a four to six day event that is usually three changes, so the preservative order is three times the first fill rather than one.

Can I make my own flower food?

A commercial flower food is a formulated product that contains a biocide as well as sugar and an acidifier, and a homemade mixture is not an equivalent. Household recipes circulate widely and can damage the flowers or the vase, so the reliable approach is to use the product the supplier sells and the dose they publish. What genuinely extends vase life is clean water in a washed vase, a fresh cut on the stem and a cool position away from direct sun.

How much flower food do I need for twenty vases?

It depends on the vase, and that is the point: twenty bulb vases holding about a litre each is 20 litres for the first fill, while twenty cylinders of the same height and width hold 34 litres. At three water changes the difference is 60 litres against 102 litres, and at 7 grams per litre that is 420 grams against 714 grams. Work from the volume rather than from a sachet per vase, because a sachet per vase overdoses a small vase and underdoses a large one.