Mastiff weight predictor
This page covers the English Mastiff — one of the heaviest breeds (males 160–230 lb, females 120–170 lb). Grows for a full ~2 years; slow, lean growth is vital for the joints.
Typical adult: 120–230 lb · grown by ~24 months
Predicted adult weight
Fully grown—
likely —
Enter your puppy’s weight and age.
That doesn’t look right
Your puppy’s growth curve
Estimated weight as they grow up — the dot is where they are now.
| Age | Est. weight |
|---|
Good to know
General guidance only — an estimate, not veterinary advice. Always check with your vet about your pet’s growth, weight and diet.
How this was calculated
For a Mastiff we use the giant-breed growth curve (matures around 24 months): adult weight ≈ current weight ÷ the fraction of adult weight a giant breed reaches at this age. Typical adult weight (120–230 lb) is from the AKC breed standard. The gauge shows where your prediction lands against the breed-typical adult range.
Source: AKC breed standard + WALTHAM growth charts. Full method on our methodology page.
Built by the PawGauge team, reviewed against cited veterinary sources. Last reviewed 29 June 2026.
About our figures →Mastiff growth chart
Typical Mastiff weight from 8 weeks to fully grown, for males and females. A healthy Mastiff tracks near these figures — individuals sit up to ~10–15% either side.
| Age | Male | Female |
|---|---|---|
| 8 weeks | 34.6 lb (16 kg) | 25.7 lb (12 kg) |
| 3 months | 55.7 lb (25 kg) | 41.5 lb (19 kg) |
| 4 months | 75.6 lb (34 kg) | 56.2 lb (25 kg) |
| 5 months | 90.8 lb (41 kg) | 67.6 lb (31 kg) |
| 6 months | 104.2 lb (47 kg) | 77.5 lb (35 kg) |
| 7 months | 118 lb (54 kg) | 87.7 lb (40 kg) |
| 8 months | 128.1 lb (58 kg) | 95.3 lb (43 kg) |
| 9 months | 138.3 lb (63 kg) | 102.8 lb (47 kg) |
| 10 months | 147.1 lb (67 kg) | 109.4 lb (50 kg) |
| 12 months | 163.9 lb (74 kg) | 121.9 lb (55 kg) |
| 14 months | 171.7 lb (78 kg) | 127.7 lb (58 kg) |
| 16 months | 179.6 lb (81 kg) | 133.5 lb (61 kg) |
| 18 months | 187.3 lb (85 kg) | 139.3 lb (63 kg) |
| 21 months | 192.9 lb (87 kg) | 143.5 lb (65 kg) |
| Adult (~24 mo) | 160–230 lb (73–104 kg) | 120–170 lb (54–77 kg) |
Mastiff growth, explained
Mastiffs are a giant breed, so they follow the giant-breed growth curve. This page covers the English Mastiff — one of the heaviest breeds (males 160–230 lb, females 120–170 lb). Grows for a full ~2 years; slow, lean growth is vital for the joints. Most reach close to their adult weight by around 24 months, then continue to firm up in muscle and chest for a while after.
To predict an adult weight we divide your puppy’s current weight by the fraction of adult weight a giant breed has typically reached at that age. Typical adult weight (120–230 lb) is from the AKC breed standard. The result is an estimate with a likely range — genetics and nutrition move individual dogs up or down. If your Mastiff looks heavier or lighter than the breed-typical band, your vet is the best person to check.
Mastiff weight questions
- How big do Mastiffs get?
- A typical adult Mastiff weighs about 120–230 lb. This page covers the English Mastiff — one of the heaviest breeds (males 160–230 lb, females 120–170 lb). Grows for a full ~2 years; slow, lean growth is vital for the joints.
- What should a Mastiff weigh by age?
- See the Mastiff growth chart above for weight at 8 weeks through to adult. As a guide, a giant-breed puppy is roughly half its adult weight by about 6 months.
- Do male and female Mastiffs weigh differently?
- Yes — male Mastiffs run about 160–230 lb and females about 120–170 lb, so the growth chart above shows a separate line for each. Individuals overlap.
- When is a Mastiff fully grown?
- Mastiffs are a giant breed and usually finish growing around 24 months, though they may keep filling out a little after that.
- How accurate is this for a Mastiff?
- Within about 10–15% if your puppy is a typical Mastiff. Crossbreeds, runts and big-boned individuals vary more. It’s an estimate — your vet can assess your individual dog.
