Diaper Size Guide Calculator
Find the right diaper size for your baby by weight in lbs or kg.
Covers Newborn through Size 7 with weight ranges for all major diaper brands.
Diaper sizing is based primarily on baby weight rather than age, because growth rates vary significantly between infants. Two babies of the same age may need diaper sizes that differ by two full sizes — always go by weight, not the age range printed on packaging.
Standard US diaper size guide by weight:
| Size | Weight (lbs) | Weight (kg) | Age Range (typical) | Avg. Daily Usage |
|---|---|---|---|---|
| Newborn (N) | Up to 10 lbs | Up to 4.5 kg | 0–1 month | 10–12/day |
| Size 1 | 8–14 lbs | 3.6–6.4 kg | 0–4 months | 8–10/day |
| Size 2 | 12–18 lbs | 5.4–8.2 kg | 2–6 months | 8–10/day |
| Size 3 | 16–28 lbs | 7.3–12.7 kg | 5–15 months | 6–8/day |
| Size 4 | 22–37 lbs | 10–17 kg | 12–30 months | 6–8/day |
| Size 5 | 27–35 lbs | 12–16 kg | 2–3 years | 5–7/day |
| Size 6 | 35+ lbs | 16+ kg | 3+ years | 4–6/day |
| Size 7 | 41+ lbs | 18.5+ kg | 3.5+ years | 4–5/day |
Sizes overlap by design: Overlapping weight ranges give you flexibility. If your baby is in the overlap zone (e.g., 12 lbs, where sizes 1 and 2 both apply), consider moving to the larger size if you’re experiencing leaks or red marks.
Signs it’s time to size up:
- Red marks or indentations on the waist or thighs after removal
- Frequent blowouts (poop escaping at the legs or waist)
- Difficulty fastening the tabs without overlap
- The diaper appears too small visually when on the baby
Signs you may need to size down:
- Large gap at the waist or thigh (leakage risk)
- Tabs overlap far past the center panel
Monthly diaper cost estimation:
Monthly Cost = Daily Usage × Cost per Diaper × 30
Cost per diaper by brand tier (2025 US average):
| Tier | Examples | Cost per Diaper |
|---|---|---|
| Budget | Kirkland, store brand | $0.12–0.18 |
| Mid-range | Luvs, Up & Up | $0.18–0.25 |
| Premium | Pampers, Huggies | $0.25–0.40 |
| Eco-friendly | Dyper, Honest, Bambo | $0.35–0.65 |
Worked example: 3-month-old baby in Size 2 (8 diapers/day), using mid-range brand at $0.22/diaper: Monthly cost = 8 × $0.22 × 30 = $52.80/month Annual cost at that rate = $633.60/year
Newborn stocking tip: Do not over-buy Newborn or Size 1 diapers before birth — many babies grow out of these within 3–6 weeks. Buy one small box first, see how the sizing fits, then stock up on the size your baby lands in.