Cephalexin For Cats Dosage Calculator · Dose by Weight

Cephalexin For Cats Dosage Calculator

Calculate the correct cephalexin dose for your cat by weight, always confirm with your veterinarian first

Setup
Always consult your veterinarian before giving your cat cephalexin. Cephalexin is a prescription antibiotic and is not appropriate for every infection. Never give your cat antibiotics left over from a previous prescription or prescribed for another pet or person.
Your cat
kg
lb
Typical adult cat weight: 3.5–5.5 kg (8–12 lb). Weigh your cat on a kitchen scale or a pet scale for the most accurate dose.
Dosage
Veterinary standard range: 15–35 mg/kg PO every 6–12 hours. The most common regimen is 15 mg/kg every 12 hours for soft tissue infections like wounds and abscesses. Severe or deep infections may need higher doses or shorter intervals.
Treatment duration
days
Skin / wound / abscess: 5 days is the standard label duration. Your veterinarian may extend this if the infection is slow to resolve.
Calculated Dose
Dose per administration
— mg
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Dose per administration
— mg
Daily total
— mg
Doses per day
—
Treatment duration
—
Product form breakdown
Cephalexin 250 mg capsule
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Cephalexin 500 mg capsule
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Cephalexin 75 mg chewable tablet (Rilexine)
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Cephalexin 50 mg/ml oral suspension
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Dose by weight — quick reference
Weight (kg)Weight (lb)15 mg/kg20 mg/kg25 mg/kg30 mg/kg35 mg/kg
Safety warnings & contraindications
Do NOT use cephalexin in cats with:
  • Known allergy or hypersensitivity to cephalosporins, penicillins, or other beta-lactam antibiotics
  • Severe kidney disease (renal insufficiency) — the dose may need to be reduced
  • Rabbits, guinea pigs, hamsters, or gerbils — cephalexin can be fatal in these species
Possible side effects — call your vet if you see:
  • Vomiting or diarrhea
  • Loss of appetite
  • Lethargy
  • Hives, facial swelling, or difficulty breathing (allergic reaction)
  • Increased thirst or urination (possible sign of kidney effects)
Administration tips:
  • Give with or without food. If your cat vomits, try giving with a small meal.
  • Complete the full course — stopping early can lead to antibiotic resistance and relapse.
  • If a dose is missed, give it when you remember and adjust the next dose accordingly. Do not double up.
  • Oral suspension should be refrigerated after reconstitution and shaken well before each dose.
  • Cephalexin can be given with or without food, but giving with food may reduce stomach upset.
Dose formula: Dose (mg) = body weight (kg) × dose rate (mg/kg). Based on the veterinary standard range of 15–35 mg/kg PO every 6–12 hours (MSD Veterinary Manual). Individual cats vary — your veterinarian may prescribe a different dose based on the infection, your cat's kidney function, and response to treatment.
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Cephalexin for Cats Dosage Calculator: Dose by Weight and Product Form

Cephalexin dosing in cats isn’t one number. It depends on your cat’s weight, the infection being treated, the dose rate your vet chose, and which product form you actually have in the house. This calculator takes all four and returns the milligrams per dose, the daily total, and how much of a 250 mg capsule, 500 mg capsule, 75 mg chewable tablet, or 50 mg/ml suspension that works out to. Always confirm the dose with your veterinarian before giving your cat anything.

Cephalexin is a first-generation cephalosporin antibiotic. Vets prescribe it for skin infections, wounds, abscesses, urinary tract infections, and some respiratory infections. The standard veterinary range is 15 to 35 mg/kg by mouth every 6 to 12 hours, and the most common starting point is 15 mg/kg twice daily for five days. That range is wide on purpose. A mild wound and a deep pyoderma don’t get the same dose, and a cat with reduced kidney function may need less than a healthy one. The calculator puts the range into a single number for your cat, so you know what a prescribed dose rate actually looks like in milligrams and in real capsule fractions.

 

How to Use the Cephalexin for Cats Dosage Calculator

  1. Pick your weight unit, then select the product form your vet prescribed. The product dropdown tells the calculator which capsules or liquid to break the dose into.

  2. Enter your cat’s current weight. Weigh at home on a kitchen scale or a pet scale if you can.

  3. Choose the dose rate. 15 mg/kg is the standard label dose; higher rates are for more serious infections.

  4. Set the frequency your vet specified: every 12 hours, 8 hours, 6 hours, or once daily.

  5. Select the condition being treated to load the typical treatment duration.

  6. Check the dose per administration in the large panel, then look at the product breakdown for capsule, tablet, and millilitre amounts.

  7. Read the verdict banner to see whether the chosen dose rate sits in the standard, moderate, or maximum band.

  8. Confirm the number with your veterinarian before the first dose. The calculator is a double-check, not a prescription.

 

How the Cephalexin for Cats Dosage Calculator Formula Works

The calculator multiplies your cat’s weight in kilograms by the chosen dose rate in mg/kg. That gives the milligrams per dose. Frequency is separate and only affects the daily total. Product breakdown divides the dose per administration by each product’s strength.

Formula: Dose per administration (mg) = body weight (kg) × dose rate (mg/kg)
Formula: Daily total (mg) = dose per administration × (24 ÷ frequency in hours)
Formula: Product amount = dose per administration ÷ product strength

Weight converts at 0.45359237 kg per pound. If you enter pounds, the tool converts to kilograms before anything else runs. The dose rate dropdown holds five values: 15, 20, 25, 30, and 35 mg/kg. Frequency holds four: every 12 hours (BID), 8 hours (TID), 6 hours (QID), and once daily (SID, which is off-label for cephalexin in cats).

ProductStrengthTypical use
Cephalexin capsule250 mgStandard small-cat dosing
Cephalexin capsule500 mgLarger cats or higher dose rates
Chewable tablet (Rilexine)75 mgPalatable, scored, easy to split
Oral suspension50 mg/mlKittens, small cats, fractional doses

Duration is preset by condition: 5 days for skin, wound and abscess, 14 days for urinary tract and respiratory infections, 28 days for deep pyoderma, or a custom number you enter. Blank or zero weight returns an invalid input message. The verdict banner changes with dose rate: 15 and 20 mg/kg read as standard, 25 mg/kg as moderate-severe, 30 mg/kg as severe, and 35 mg/kg as maximum.

 

Worked Example: A 3.8 kg Cat With a Bite Wound Abscess

Your cat weighs 3.8 kg and has a draining abscess from a fight. The vet prescribes 15 mg/kg twice daily for 5 days.

  1. Dose per administration: 3.8 × 15 = 57 mg

  2. Daily total: 57 × 2 = 114 mg per day

  3. 250 mg capsule: 57 ÷ 250 = 0.228 of a capsule

  4. 75 mg chewable tablet: 57 ÷ 75 = 0.76 of a tablet

  5. 50 mg/ml suspension: 57 ÷ 50 = 1.14 ml per dose

At 57 mg per dose, the 250 mg capsule is too large to split accurately. The chewable tablet gives you roughly three-quarters of a 75 mg tablet, which is easier with a scored tablet and a pill cutter. The suspension gives 1.14 ml, which is a clean measurement with a dosing syringe. This is exactly the situation where the product form matters as much as the dose. Same cat, same dose, three different practical answers.

Now raise the dose rate to 30 mg/kg for a deep infection. Dose per administration jumps to 114 mg. That’s 1.52 of a 75 mg tablet, or 2.28 ml of the 50 mg/ml suspension. The 250 mg capsule is still too large. The suspension becomes the most accurate option at that dose for a cat this size.

Understanding Cephalexin Dosing in Cats

 

What Is the Standard Cephalexin Dosage for Cats?

The standard range is 15 to 35 mg/kg by mouth every 6 to 12 hours. The most common regimen, and the one that matches the label on veterinary products like Rilexine and Therios, is 15 mg/kg twice daily. Severe infections may go up to 30 or 35 mg/kg, sometimes at shorter intervals.

The dose your vet picks depends on the infection and the cat. A superficial wound gets 15 mg/kg twice daily for five days. A urinary tract infection usually gets the same rate for 14 days. A deep pyoderma may need 25 to 30 mg/kg for 28 days or longer. The range exists because cephalexin is effective across it, and vets adjust within it based on how the infection responds.

 

How Do You Calculate Cephalexin Dose by Weight?

Multiply the cat’s weight in kilograms by the prescribed mg/kg rate. A 4.5 kg cat at 15 mg/kg needs 67.5 mg per dose. At 25 mg/kg, the same cat needs 112.5 mg per dose. If you’re working in pounds, convert to kilograms first: divide the weight in pounds by 2.2046.

Frequency doesn’t change the per-dose amount. It changes the daily total. A 67.5 mg dose given twice daily is 135 mg per day. The same dose given three times daily is 202.5 mg per day. That’s why the calculator shows both numbers.

 

How Much Cephalexin Is in a 250 mg Capsule for a Cat?

A 250 mg capsule contains 250 mg of cephalexin. The question is how much of it your cat needs. A 4 kg cat at 15 mg/kg needs 60 mg, which is 0.24 of a capsule. That’s less than a quarter, and quartering a capsule is unreliable. The contents spill, the split is uneven, and you can’t guarantee the dose.

This is the most common practical problem with cephalexin in cats. The capsules are designed for human-sized doses, and most cats need fractions. If your vet prescribes a dose below about 125 mg, ask whether the chewable tablet or oral suspension would be easier. Both measure more accurately at small doses.

 

What Is the Dose of Cephalexin for a Cat in ml?

That depends on the suspension concentration. A 50 mg/ml suspension delivers 50 mg of cephalexin per millilitre. A 60 mg dose needs 1.2 ml. A 100 mg dose needs 2 ml. If the suspension is a different strength, the volume changes accordingly.

Use the dosing syringe that comes with the suspension rather than a kitchen teaspoon. A teaspoon holds roughly 5 ml, but the actual volume varies by spoon and by how full you fill it. For a 1.2 ml dose, a syringe is the only reliable option.

 

What Is the Cephalexin Dose for a Cat in mg/kg?

The veterinary standard is 15 to 35 mg/kg per dose. The lower end, 15 mg/kg, is the label dose for soft tissue infections. The middle, 20 to 25 mg/kg, covers moderate infections. The top end, 30 to 35 mg/kg, is reserved for severe or deep infections and may be given more frequently.

Some references list 10 mg/kg as a minimum for very mild cases, and some compounded products are dosed at 30 mg/kg once daily. Those are variations on the same range, not separate standards. Follow the number your vet wrote on the prescription.

 

How Long Should You Give Cephalexin to a Cat?

Five days for a simple wound or abscess. Fourteen days for a urinary tract or respiratory infection. Twenty-eight days or longer for deep pyoderma. Your vet may adjust based on how quickly the infection clears.

The rule is to finish the full course even if the cat looks better in two days. Stopping early is the fastest way to leave surviving bacteria behind and encourage resistance. If your cat won’t take the medication or keeps spitting it out, call the vet rather than skipping doses.

 

What Are the Side Effects of Cephalexin in Cats?

The most common side effects are vomiting and diarrhea, and they’re often mild and short-lived. Loss of appetite, drooling, and lethargy also show up. These signs are more likely at higher dose rates, and they usually ease if you give the medication with a small meal.

More serious reactions are rare but possible. Hives, facial swelling, and difficulty breathing suggest an allergic reaction and need immediate veterinary attention. Fever, pale gums, and unusual tiredness can also signal a problem. Call your vet if any of those appear.

 

Can You Give a Cat Human Cephalexin?

The drug is the same molecule, and vets routinely prescribe human-labelled cephalexin because it’s often cheaper than veterinary products. The problem is dosing, not the drug. Human capsules come in 250 mg and 500 mg strengths, and most cats need a fraction of one.

Splitting a capsule accurately is hard. You also need a prescription, because giving antibiotics without veterinary direction risks the wrong drug, the wrong dose, and antibiotic resistance. Talk to your vet first. If they’re happy with human cephalexin, ask them to write the dose in milligrams so you can check the math.

 

Which Cats Should Not Take Cephalexin?

Cats with a known allergy to cephalosporins, penicillins, or other beta-lactam antibiotics should not get cephalexin. Cats with severe kidney disease may need a reduced dose, because the drug is cleared through the kidneys. Kittens under 9 weeks and cats weighing under 2 kg are outside the labelled use for some veterinary products.

The most serious warning is for small pets other than cats and dogs. Cephalexin can be fatal in rabbits, guinea pigs, hamsters, and gerbils. If you have a multi-pet household, keep the medication well away from them.

Disclaimer

This calculator estimates a cephalexin dose from a weight and a dose rate you enter. It is not a prescription and it does not replace veterinary judgment. Cephalexin is a prescription antibiotic, and the correct dose depends on the infection, your cat’s kidney function, and how your cat responds to treatment. Never give your cat leftover antibiotics, antibiotics prescribed for another pet or person, or a dose you calculated without veterinary confirmation. Cats with known beta-lactam allergies, severe kidney disease, or that weigh under 2 kg may need different handling. Do not give cephalexin to rabbits, guinea pigs, hamsters, or gerbils, as it can be fatal in those species. If your cat shows hives, facial swelling, difficulty breathing, or repeated vomiting after a dose, contact your veterinarian immediately.

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