Oxalic Acid Dosage Calculator
Pick the method and the product on your shelf, enter your colonies, and get the dose the label allows: grams per brood chamber for vaporizing, millilitres per colony for the dribble, and how much to mix. Free, no signup, all math in your browser.
Application method
Per colony
8 g oxalic acid dihydrate
4 g × 2 brood chambers.
All 2 colonies: 16 g.
The label on your package is the law, not this page. These numbers are US EPA labels as accepted on the dates shown. Labels change, some states issue their own directions, and outside the US the authorised products and doses are different. Follow your local label and regulations.
A seam is the gap between two frames with bees in it — count the ones you can see bees in when you look down from above, in every brood box. Vaporization doses are per brood chamber, not per colony: a double deep gets two box doses.
Treat when there is little or no brood
Oxalic acid reaches mites riding on adult bees. It does not reach the ones under cappings, so the labels say to use it when little or no brood is present. The Honey Bee Health Coalition lists brand-reported efficacy of 82–99% when brood is not present and calls it less effective with capped brood. That makes the natural windows:
- Late autumn and early winter, when the queen has stopped laying and the last capped brood has emerged — the “broodless reset” most rotation plans end the year with.
- Packages and swarms, which have no brood yet. The labels name both.
- An induced brood break. Confining the queen stops new brood; Berry et al. (2023) caged queens for 14 days before vaporizing in summer and reported about five times the mite mortality of vaporizing without the break.
With brood present, the labels say several treatments a few days apart are needed and to follow state and extension guidance. WSU Extension notes a study where seven vaporizations at 1 g per brood chamber, every five days, still did not control mites during brood rearing — repeating a low dose is not a substitute for the broodless window. Whatever you do, run a second mite wash afterwards and put both counts through the varroa calculator.
Safety the labels require
Oxalic acid is labelled Danger — Poison: corrosive, causes irreversible eye damage, and may be fatal if inhaled. The labels list the equipment by method:
Dribble
Long sleeves and long pants, socks and shoes, chemical-resistant gloves, goggles, and at least a NIOSH-approved particulate filtering facepiece respirator.Vaporization
The same clothing and gloves, goggles or a face shield, and at least an elastomeric half-mask respirator with acid gas cartridges and N, R or P filters. A dust mask is not enough.- Vaporize only outdoor colonies, through a restricted lower entrance, with upper entrances and cracks taped shut. Never in an enclosed overwintering building.
- Dissolve dribble crystals in warm syrup so they fully dissolve. The labels warn the dribble can cause some bee loss in weak colonies or poor overwintering conditions.
- The Coalition notes no temperature restriction but flags the risk of opening a hive below 40 °F (4 °C), and that a tight cluster may reduce effectiveness.
Follow your local label and regulations. This page transcribes US EPA labels on the dates listed below. The package in your hand is the legal instruction; some states issue their own directions, and outside the US the authorised products and doses differ. When they disagree with this page, they win.
Where the oxalic treatment fits in a 3-year rotation
The rotation table that ends every year with the broodless oxalic reset, the wash test that tells you whether a treatment worked, and a per-hive log. One email, then print it.
Oxalic acid dosing questions
How much oxalic acid do I vaporize per hive?
It depends on the product label, and the dose is per brood chamber, not per hive. The current Api-Bioxal label (amended June 2025) says 4.0 g per brood chamber; packages printed under the older label say 1.0 g. The current EZ-OX label (amended January 2026) says 2 g per deep brood chamber for typical infestation and 4 g for higher infestation, with 4 g the maximum. A double deep gets two box doses.
What is the oxalic acid dribble dose?
Dissolve 35 g of oxalic acid dihydrate in 1 litre of warm 1:1 sugar syrup (Api-Bioxal label) or 2 g in a quarter cup, 59 mL (EZ-OX label). Trickle 5 mL onto the bees in each occupied seam, in every brood box, up to a maximum of 50 mL per colony whether it is a nuc or a double deep. The premixed Api-Bioxal RTU is also 5 mL per occupied seam, without the 50 mL ceiling.
Does oxalic acid work when there is brood in the hive?
Not well. The labels say to use it when little or no brood is present because it does not reach mites under cappings. The Honey Bee Health Coalition lists brand-reported efficacy of 82 to 99% when brood is not present and calls it less effective with capped brood. With brood present, the labels say several treatments days apart are needed and to follow state and extension guidance.
Can I use oxalic acid with honey supers on?
The current US labels for Api-Bioxal and EZ-OX say oxalic acid can be used when honey supers are on the hive. Older labels and some state rules have said otherwise, so check the package you hold and your state.
What protective equipment does oxalic acid need?
For the dribble, the labels require a long-sleeved shirt and long pants, socks and shoes, chemical-resistant gloves, goggles and at least a NIOSH-approved particulate filtering facepiece respirator. For vaporizing, the respirator must be at least an elastomeric half mask with acid gas cartridges and N, R or P filters, and the eye protection can be goggles or a face shield.
Sources
- Api-Bioxal, EPA Reg. No. 73291-2 — label amendment accepted 24 June 2025 (4.0 g vaporizer rate)
- Api-Bioxal, EPA Reg. No. 73291-2 — previous label, 14 May 2024 (1.0 g vaporizer rate)
- EZ-OX, EPA Reg. No. 101743-2 — label amendment accepted 27 January 2026 (2–4 g vaporizer rate)
- Honey Bee Health Coalition, Tools for Varroa Management, 9th edition (June 2026) — oxalic acid product pages and the Api-Bioxal RTU summary
- Washington State University Extension FS403E, Oxalic Acid Options for Controlling Varroa destructor (July 2025)
- Berry et al. 2023, Inducing a summer brood break increases the efficacy of oxalic acid vaporization, J. Insect Sci. 23(6):14
Labels read 22 September 2026.
Related tools and reading
Varroa Mite Treatment Calculator
Wash count → infestation % against the seasonal threshold, and before/after efficacy.
Sugar Syrup Ratio Calculator
Need the 1:1 syrup for a dribble? Sugar in, water and finished volume out.
Oxalic Acid Timing and the Broodless Window
How to check whether a colony is actually broodless before you treat.
Varroa Mite Treatment Guide
Oxalic, formic, amitraz and thymol — when each one fits.
Keep the treatment record with the mite counts
HiveSense logs each treatment, dose and date per hive next to the washes before and after it — offline, in the yard.
More free beekeeping tools