Baby Weight Converter
Convert birth weight between grams, kilograms, and pounds and ounces — correctly. Enter any value and all three update instantly.
Why this calculator shows ounces correctly
Most online converters display baby weight as decimal pounds — for example, 3.4 kg becomes 7.5 lbs or 7.49 lbs. That is not a weight anyone recognises or can use. It is a fraction, not a measurement.
This calculator always converts to whole pounds and whole ounces — because that is how families ask, remember, and share a baby's birth weight. Clinical records use grams or kilograms; this converter is for the moment a grandparent asks "but how much is that in pounds?"
Common birth weight reference
| Grams | Kilograms | Pounds & Ounces | Note |
|---|---|---|---|
| 1000 g | 1.000 kg | 2 lbs 3 oz | Very preterm threshold |
| 1500 g | 1.500 kg | 3 lbs 5 oz | Preterm — intensive care |
| 2000 g | 2.000 kg | 4 lbs 7 oz | Preterm — special care |
| 2500 g | 2.500 kg | 5 lbs 8 oz | Low birthweight threshold |
| 3000 g | 3.000 kg | 6 lbs 10 oz | Normal range |
| 3175 g | 3.175 kg | 7 lbs 0 oz | 7 pounds exactly |
| 3400 g | 3.400 kg | 7 lbs 8 oz | Average NZ birth weight |
| 3500 g | 3.500 kg | 7 lbs 11 oz | Normal range |
| 4000 g | 4.000 kg | 8 lbs 13 oz | Large for gestational age threshold |
| 4500 g | 4.500 kg | 9 lbs 15 oz | Macrosomia threshold |
Customised centiles & NZ clinical guidance
In Aotearoa New Zealand, birthweight is assessed against customised centiles generated by the GROW (Gestation Related Optimal Weight) software, used as part of the national Aotearoa Growth Assessment Programme (GAP), commissioned nationally by Te Whatu Ora. Unlike fixed population charts, GROW customises each pregnancy's growth potential based on maternal height, pre-pregnancy weight, ethnicity, and parity — giving a more clinically meaningful picture of whether a baby has grown to their individual potential.
<10th centile — Small for Gestational Age (SGA): triggers SGA/FGR monitoring pathway
10th–90th centile — Within expected growth potential
>90th centile — Large for Gestational Age (LGA): assess for macrosomia risk and gestational diabetes
The fixed weight thresholds in the table above (e.g. 2500 g for low birthweight, 4000 g for LGA) are internationally recognised population-based reference points. In NZ clinical practice, SGA and LGA classification uses customised GROW centiles — so a baby's actual weight may fall within the population "normal range" while still being below or above their individualised growth potential.
Postnatal weight loss — Starship guidance: After birth, some weight loss is normal and expected. Starship Clinical Guidelines for weight loss in newborns recognise weight loss up to 7% of birth weight as within the expected range for term newborns. Weight loss >7% warrants increased feeding assessment and monitoring. Weight loss ≥10% is a clinical threshold requiring review — with consideration of supplementation, lactation assessment, clinical condition, and hydration status.
References: Aotearoa Growth Assessment Programme (GAP), Perinatal Institute; NZ GROW 2.0; Starship Clinical Guidelines — Weight loss in newborns.
About this tool
This calculator was built by a New Zealand midwife to solve a daily frustration: no freely available converter displayed birth weight in whole pounds and ounces — the way families actually ask for it.
New Zealand uses metric weights in clinical documentation. Pounds and ounces remain the way many families — particularly those from the United Kingdom, United States, Pacific Island communities, and older generations — understand and remember birth weight. Being able to give a clear conversion is part of good communicative care.
More midwifery calculators are in development. If you have a conversion or tool you find yourself calculating repeatedly, let us know.