Formulas and sources

How it works

• Cats and dogs both use 70 × BW^0.75. The linear 30 × BW + 70 is not used: it only applies from 2 to 45 kg, and mixing the two gives one cat two numbers.
• Factors from AAHA 2021 Box 1, cat / dog: neutered adult 1.2–1.4 / 1.4–1.6; intact adult 1.4–1.6 / 1.6–1.8; obese-prone or inactive 1.0 / 1.0–1.2; weight loss 0.8 / 1.0; growth 2.5 / 3.0 under 4 months, 2.0 from 4 months.
• Ranges prefill their low end and can be changed. Gestation, lactation and working dogs are not prefilled: the ranges are too wide, so the factor comes from the vet.
• Nothing is rounded until display. RER and DER are shown as whole kcal/day.

Sources

1. AAHA 2021 Nutrition and Weight Management Guidelines for Dogs and Cats, Box 12021

How it works

• 143 Hill’s and Royal Canin prescription diets: 67 for cats and 76 for dogs. The cat and dog versions of a diet are kept apart, because their energy differs.
• Energy values are the ones each manufacturer publishes. Each food shows its source page, the country of that page and the date it was checked.
• Where Royal Canin gives no kcal per can, it is worked out from kcal/kg × can weight, and the result says so.
• Cans are shown to ¼ can, grams to whole grams.

Basis

Hill’s Pet Nutrition and Royal Canin published product information. Each food in the app lists its own source page and check date (cat diets checked 2026-10-18).

How it works

• Maintenance and the juvenile factors are from AAHA 2024 Table 9; the deficit is Box 3. The per-kg method is preselected, as in AAHA’s own Table 11 example (10 kg dog, 60 mL/kg/day = 25 mL/hr).
• Table 9’s third method (30 × BW + 70) is not used: its unit is printed as mL/kg/day, which would give a 10 kg dog 3700 mL a day.
• The deficit is replaced over 12 to 24 hours. Above 12% dehydration, AAHA Table 3 describes hypovolemic shock, and a warning says to treat shock first.
• Giving sets: 10, 15, 20 or 60 drops per mL. Rates are shown to 0.1 mL/hr, drops as whole numbers.

Sources

1. Pardo M, Spencer E, Odunayo A, et al. 2024 AAHA Fluid Therapy Guidelines for Dogs and Cats. J Am Anim Hosp Assoc 2024;60:131–163, Box 3, Tables 3, 9 and 112024
2. Drip rate formula: University of Essex, Drip Rates Booklet

How it works

• The dose and the vial strength are entered from the vet’s order and the label. Vetrule holds no dose data.
• Volumes follow syringe marks: 0.01 mL below 1 mL, 0.1 mL from 1 to 10 mL, 1 mL from 10 mL.
• Below 0.01 mL the result reads “< 0.01”, never 0. If rounding to the marks moves the dose by more than 5%, a warning appears.
• Totals under 1 mg are shown in µg to three significant figures, so a 1000-fold unit slip stands out.

Basis

Arithmetic only, on the vet’s order and the vial label. 1% w/v = 1 g per 100 mL = 10 mg/mL.

How it works

• In Grubb’s formula A is the dose, B body weight, C the final volume in mL, D the rate in mL/hr and E the strength in mg/mL. For mg/kg/hr, drop the 60 and the 1000.
• The dose-rate unit has no default and must match the order: per minute and per hour differ 60-fold.
• Syringe: the diluent is always shown as “fill to N mL”, the full syringe volume, not as a second amount to measure.
• Fluid bag: first remove the same volume of fluid from the bag as the drug you add (Grubb, Table 3). With the drip rate in mL/kg/hr, body weight cancels out.
• Fluid bag: changing the drip rate changes the dose. Grubb: “If the infusion rate is halved, the amount of lidocaine in the bag should be doubled to keep the dose constant.” This note stays on screen.
• Checked against Grubb’s Table 3 lidocaine grid and a vetprep example: 20 kg dog, fentanyl 4 µg/kg/hr, 50 µg/mL → 1.6 mL/hr undiluted.

Sources

1. Grubb T. Constant Rate Infusions: Don't Cry – Use CRI. IVAPM2023
2. vetprep, Constant Rate Infusions in Small Animal Veterinary Medicine (worked examples)

How it works

• Mass: kg, g, mg, µg, lb, oz. Volume: L, mL, µL, fl oz, teaspoon, tablespoon, cc. Temperature: °C, °F. Concentration: %, mg/mL, µg/mL.
• Teaspoon and tablespoon use the medical definitions (5 and 15 mL), not the US 4.93 mL.
• Lab-value SI conversions (mg/dL ↔ mmol/L) are not in version 1.0.

Basis

Exact unit definitions (1 lb = 0.45359237 kg by definition).

How it works

• Blood volume prefills 90 mL/kg for dogs, the value validated by Short 2012, and 60 mL/kg for cats (BSAVA Manual, via Reed 2014). Both can be changed.
• Target PCV and unit PCV have no defaults: the target is the vet’s order, the unit PCV comes from the bag label.
• Above half the estimated blood volume, a warning gives the massive-transfusion definition: more than one blood volume in 24 hours, or half a blood volume in 3 hours (Jutkowitz 2002).
• In cats no formula was accurate (Reed 2014); with 60 mL/kg the volume usually comes out a little high.
• No per-kg maximum is applied: the sources give none.

Sources

1. Blois SL. Blood Transfusions in Dogs and Cats. Merck Veterinary Manual (reviewed 2024)2024
2. Short JL, Diehl S, Seshadri R, Serrano S. Accuracy of formulas used to predict post-transfusion packed cell volume rise in anemic dogs. J Vet Emerg Crit Care 2012;22(4):428–4342012
3. Reed N, Espadas I, Lalor SM, Kisielewicz C. Assessment of five formulae to predict post-transfusion packed cell volume in cats. J Feline Med Surg 2014;16(8):651–6562014
4. Jutkowitz LA, et al. Massive transfusion in dogs: 15 cases (1997–2001). JAVMA 2002;220(11):1664–1669. PMID 120515072002
5. DoveLewis. Guidelines for Use of Canine / Feline Blood Components2018

How it works

• BSA is shown to three decimals, rounded half up. The dose uses the unrounded BSA.
• The formula reproduces every row of the Merck tables to 0.001 m²: 60 rows for dogs (0.5–55 kg) and 20 for cats (0.5–10 kg).
• Cats use K = 10.0, as in the Merck table and the oncology textbook Girens cites, not the 10.4 found on uncited web pages.
• For a dog under 15 kg with a mg/m² dose, a note says mg/m² dosing can give small dogs a relatively high dose, because higher toxicity has been observed in small dogs dosed by mg/m² (Arrington 1994; Page 1988; the 15 kg convention as reported by Girens 2019). The result is not blocked.
• The dog formula was derived in 1911 from six puppies; CT-measured BSA differed from it by −9% to +19% (Girens 2019).

Sources

1. Merck Veterinary Manual, Weight to Body Surface Area Conversion for Dogs
2. Merck Veterinary Manual, Weight to Body Surface Area Conversion for Cats
3. Girens R, et al. Use of computed tomography and radiation therapy planning software to develop a novel formula for body surface area calculation in dogs. J Vet Intern Med 2019;33(2):792–7992019
4. Arrington KA, et al. Comparison of body surface area-based and weight-based dosage protocols for doxorubicin administration in dogs. Am J Vet Res 1994;55(11):1587–1592. PMID 78799831994
5. Page RL, et al. Unexpected toxicity associated with use of body surface area for dosing melphalan in the dog. Cancer Res 1988;48(2):288–290. PMID 33350061988

How it works

• Base fluid potassium (AAHA 2024 Table 8): 0.9% NaCl 0; LRS 4; Plasma-Lyte A 5; Plasma-Lyte 148 5; Normosol-R 5 mEq/L. Other fluids are entered from the label.
• KCl strength is required and has no default: 1 mEq/mL and 2 mEq/mL are both in use, even within one country.
• Above 0.5 mEq/kg/hr the result is blocked until the user confirms it is the vet’s order. Exactly 0.5 is allowed: AAHA 2024 (p. 147) says the rate should not exceed 0.5 mEq/kg/hr.
• The rate is worked out from the KCl volume as shown (0.01 mL below 1 mL, 0.1 mL above), so the number on screen matches what is drawn up.
• The added KCl volume is not counted, as in AAHA 2024 Table 11, Hoehne 2015 and Cook & Heinz 2022. This errs on the safe side: the real concentration is slightly lower.
• No sliding-scale table is built in. Fixed reminders: invert the bag to mix after adding KCl, and never bolus fluids with KCl added (AAHA 2024).

Sources

1. Pardo M, Spencer E, Odunayo A, et al. 2024 AAHA Fluid Therapy Guidelines for Dogs and Cats. J Am Anim Hosp Assoc 2024;60:131–163, p. 147 and Tables 8, 112024
2. Davis H, et al. 2013 AAHA/AAFP Fluid Therapy Guidelines for Dogs and Cats. J Am Anim Hosp Assoc 2013;49:149–159 (AAFP Implementation Toolkit reprint)2013
3. Hoehne SN, Hopper K, Epstein SE. Accuracy of potassium supplementation of fluids administered intravenously. J Vet Intern Med 2015;29(3):834–8392015
4. Cook A, Heinz J. Evaluation and Management of the Hypokalemic Patient. Today’s Veterinary Practice, July/August 2022 (worked example)2022

How it works

• Pick the unknown (C1, V1, C2 or V2); V1, the stock to draw up, is preselected.
• Dilute to the final volume, not with a fixed volume. The Pharmaceutical Journal: “dilute 10mL to 100mL” ends at 100 mL, “dilute 10mL with 100mL” at 110 mL.
• % means w/v (g per 100 mL). If both strengths are in %, v/v works too.
• No result when C2 ≥ C1 or V1 ≥ V2.

Sources

1. Kumwenda L, et al. Medication maths: dilutions. The Pharmaceutical Journal 2025;314(7995)2025
2. University of Kent Student Learning Advisory Service. At a Glance: Pharmacy Calculations — C1V1 = C2V2

How it works

• The mL/kg field starts empty: the volume is the vet’s order. Vetrule does not suggest how much or how many boluses.
• A warning appears when the total is above 90 mL/kg (dogs) or 55 mL/kg (cats), the upper end of the full shock dose in the 2013 AAHA/AAFP guidelines (80–90 and 50–55 mL/kg). The 2024 guidelines give no total.
• A note, not a block, when one bolus is above the AAHA 2024 range (p. 138): 15–20 mL/kg for dogs and 5–10 mL/kg for cats, over 15–30 min, repeated if needed.

Sources

1. Pardo M, Spencer E, Odunayo A, et al. 2024 AAHA Fluid Therapy Guidelines for Dogs and Cats. J Am Anim Hosp Assoc 2024;60:131–163, p. 1382024
2. Davis H, et al. 2013 AAHA/AAFP Fluid Therapy Guidelines for Dogs and Cats. J Am Anim Hosp Assoc 2013;49:149–159 (AAFP Implementation Toolkit reprint)2013

How it works

• The default is the formula Dugger 2014 recommends after comparing 18 formulas in 250 dogs. Cats use the same formula; the validation study was in dogs.
• The alternative is the one in Cornell eClinPath and the Five-Minute Veterinary Consult. The two differ by 2 × K, so the result always names the formula used.
• Factors are 18 and 2.8 as published. Other solutes (ethylene glycol, mannitol) are not included, so a measured value can be higher.
• No reference range is shown.

Sources

1. Dugger DT, Epstein SE, Hopper K, Mellema MS. A comparison of the clinical utility of several published formulae for estimated osmolality of canine serum. J Vet Emerg Crit Care 2014;24(2):188–1932014
2. Cornell University eClinPath, Fluid changes (Osmolality)
3. Fleming M. Hyperosmolarity. In: Five-Minute Veterinary Consult: Canine and Feline, 6th ed.

How it works

• The chart is from the 2010 AAFP–AAHA guidelines (p. 71). The points under one year follow International Cat Care’s split of the chart’s ranges (2–3 months = 2–4 years, 4 months = 6–8 years).
• Life stages from the 2021 AAHA/AAFP guidelines: kitten, birth to under 1 year; young adult, 1–6 years; mature adult, 7–10 years; senior, over 10 years (a cat of exactly 10 is mature). The stages cited are listed under the result.
• The chart ends at 25 years. Up to 30 years the line continues at 4 years per year and is marked as beyond the chart; over 30 is treated as an input error.
• Human age is a rough guide for talking with owners. The chart has no research basis, and the 2021 guidelines dropped it. Age conversion for dogs is not offered: there is no accepted cross-breed standard.

Sources

1. Hoyumpa Vogt A, Rodan I, Sparkes A, et al. AAFP–AAHA Feline Life Stage Guidelines. J Am Anim Hosp Assoc 2010;46:70–85 (p. 71)2010
2. Quimby J, Gowland S, Carney HC, et al. 2021 AAHA/AAFP Feline Life Stage Guidelines. J Feline Med Surg 2021;23(3):211–2332021
3. International Cat Care, How to tell your cat’s age in human years

How it works

• Dates are counted in calendar days. The app does not judge pregnancy or read progesterone values; the vet decides the reference date.
• First breeding gives no most-likely date: breeding dates correlate less closely with whelping than ovulation does (Merck), and the window is 15 days wide.
• For cats, Merck counts 64–66 days from the LH surge triggered by copulation; the app counts from the first mating. Root Kustritz 2006 reports an average of 65.6 days, range 52–74, shown as background.

Sources

1. Davidson AP. Whelping and Queening in Dogs and Cats. Merck Veterinary Manual (reviewed 2025)2025
2. Concannon PW. Physiology and Clinical Parameters of Pregnancy in Dogs. WSAVA2002
3. Romagnoli S. Recent Advances in Canine Female Reproduction. WSAVA2006
4. Root Kustritz MV. Clinical management of pregnancy in cats. Theriogenology 2006;66(1):145–1502006