Sugar syrup calculator for bees: 1:1 and 2:1

A gallon of water does not make a gallon of syrup. With 8.35 lb of sugar it makes 1.63 US gallons of 1:1, and with 16.7 lb it makes 2.26 US gallons of 2:1. If you know what your feeder holds, you need the sum run the other way. The calculator below starts from the finished syrup, the sugar you have or the water you will use, by weight or by volume, and answers in metric, US and UK units.

I develop Crownboard, an iPhone app for hive inspection records, which has a tap for noting that you fed syrup. The calculator and the notes on this page work without the app.

Calculator

The fields start with example values. Replace them with your own.

Sugar and water for common amounts

These are by weight. Weigh the sugar. The water is shown by volume because a litre of water weighs about a kilogram.

1:1 by weight

2:1 by weight

Starting from the bag instead, 1 kg of sugar makes 1.63 L of 1:1 or 1.13 L of 2:1, and a 25 lb bag makes 4.87 US gallons of 1:1 or 3.39 US gallons of 2:1.

Is the ratio by weight or by volume?

By weight, where the source says. Michigan State University Extension bulletin E-3369 writes thin syrup as 50% sugar, one pound of sugar to one pound of water, and fall syrup as at least 66%, two parts sugar to one part water. Those percentages only hold by weight. The University of Arizona Extension publication gives the same two ratios without saying which it means, and plenty of recipes measure in cups.

The two are not the same recipe. Honey Bee Suite puts a US cup of white sugar at about 200 g, and a cup of water weighs about 237 g, so a cup of sugar weighs less than a cup of water does. Two cups of sugar to one of water is 1.69 to 1 by weight.

The sources differ on whether that matters. Honey Bee Suite argues that the bees do not care about a difference this small. The Michigan State bulletin asks for at least 66% for fall feeding, which 2:1 by volume does not reach. A kitchen scale removes the question, so use the weight setting if you have one.

The arithmetic

1:1 by weight: kilograms of sugar = litres of finished syrup × 0.615, and litres of water = litres of finished syrup × 0.615.

2:1 by weight: kilograms of sugar = litres of finished syrup × 0.884, and litres of water = litres of finished syrup × 0.442.

Both come from the density of sugar solutions at 20 °C in a US National Bureau of Standards table. A litre of 50% syrup weighs 1.23 kg, half of it sugar. A litre of 66.7% syrup weighs 1.33 kg, two thirds of it sugar. If you start from the sugar or the water, the recipe needs no density at all: at 1:1 use the same weight of water as sugar, and at 2:1 use half the weight. The density only tells you how much syrup you end up with.

One check against a published figure: the University of Arizona publication says a gallon of 2:1 can increase a colony's food reserves by seven pounds. The calculator finds 7.38 lb of sugar in a US gallon of 2:1 by weight and 6.83 lb by volume, so the figure fits either and does not settle which is meant.

The calculator treats a litre of water as one kilogram and a level US cup of sugar as 200 g. Syrup volumes assume all the sugar has dissolved, so read them as close estimates. It covers only 1:1 and 2:1, not the 1:2 mix the Arizona publication also mentions.

Which sugar, and what not to do

• Use white granulated sugar. The University of Arizona publication says "Use only white granulated sugar" for syrup.
• Not brown sugar or powdered sugar. Slides by Gary Keuffer of the Brown County Beekeepers Association, hosted on Ohio State University's Warren County site, rule out both by name.
• Do not boil the syrup. The Arizona publication says boiled syrup can burn without you noticing and form hydroxymethylfurfural, which is toxic to bees. It also says water from the hot tap is enough to get heavy syrup into solution.
• Mind the honey supers. The Keuffer slides say not to feed with honey supers on.

Which ratio when

Both university publications use thin syrup in spring and heavy syrup in fall. Michigan State ties thin syrup to spring and early summer, as a stand-in for a nectar flow, and heavy syrup to fall, because by then the bees have too little time and warmth left to dry a thinner syrup down. The bulletin's date for finishing fall feeding, October 1, is for Michigan. Your dates depend on your climate, so ask a local association or bee inspector.

Writing down what you fed

Crownboard has a Fed syrup action among the standard actions on an inspection, tapped rather than typed, and the free-text field and the notes are there for the ratio and the amount. It does not calculate syrup, keep a recipe or suggest when or how much to feed. A feeding reminder is one you write yourself.

Crownboard is free to download for iPhone with iOS 18 or later, in English. Two active hives include every feature; one optional purchase, paid once and never renewed, removes the two-hive limit.