# Dosage by weight calculator

> Dose by weight from a mg/kg rate and body weight, capped at the single and daily maximum, with the liquid volume in mL for a given strength.

Phiên bản tương tác: https://www.calcopenly.com/vi/health/dosage-by-weight-calculator
Chủ đề: Máy tính sức khỏe và thể chất

A weight-based dose is body weight in kilograms times the prescribed rate in mg/kg, given either per dose or per day and divided into doses. The result is capped at the maximum single dose and at the daily maximum divided by the number of doses, whichever is lower. For a liquid it is converted to millilitres with the product strength: dose × mL ÷ mg.

It is used to check a calculated dose against a prescription or product label. With the defaults, 20 kg at 15 mg/kg gives 300 mg, which is 9.38 mL of a 160 mg per 5 mL liquid, taken 4 times a day for 1,200 mg in total.

The rate, the maximums and the strength must come from the prescription or the label; the calculator holds no dosing information for any medicine. The BNF for Children notes that a calculated child's dose should not exceed the adult maximum, which is why the caps apply.

## Dữ liệu đầu vào

- **Weight**
- **The mg/kg figure is** (lựa chọn: Per dose, Per day, split into doses)
- **Dose rate**
- **Doses per day**
- **Maximum single dose**: From the label or prescription; leave blank if none is given.
- **Maximum per day**
- **Liquid strength: amount**: E.g. 160 mg in 5 mL. Leave both blank for tablets.
- **Liquid strength: per volume**

## Kết quả

- Calculated dose (mg) — kết quả chính
- Liquid volume per dose (mL)
- Every
- Total per day (mg)
- Weight-based dose before limits (mg)
- Limit applied

## Công thức

$$
\text{dose} = \min\!\Big(w \cdot r,\ \text{max}_{\text{single}},\ \frac{\text{max}_{\text{day}}}{n}\Big),\qquad V = \text{dose} \times \frac{\text{mL}}{\text{mg}}
$$

## Ví dụ có lời giải

### 20 kg at 15 mg/kg, 160 mg/5 mL

- Weight: 20 kg
- The mg/kg figure is: Per dose
- Dose rate: 15 mg/kg
- Doses per day: 4
- Maximum single dose: 1000 mg
- Maximum per day: 4000 mg
- Liquid strength: amount: 160 mg
- Liquid strength: per volume: 5 mL
- **Calculated dose: 300 mg**
- **Liquid volume per dose: 9.38 mL**
- **Total per day: 1,200 mg**
- **Limit applied: None**
- **Every: 6 h**
- Nguồn đối chiếu: Python 3.8 decimal: 20 × 15 = 300 mg; 300 × 5 / 160 = 9.375 mL; 300 × 4 = 1200 mg; 24 h / 4 = 21600 s

### Edge: single-dose cap reached

- Weight: 80 kg
- The mg/kg figure is: Per dose
- Dose rate: 15 mg/kg
- Doses per day: 4
- Maximum single dose: 1000 mg
- Maximum per day: 4000 mg
- Liquid strength: amount: 100 mg
- Liquid strength: per volume: 1 mL
- **Weight-based dose before limits: 1,200 mg**
- **Calculated dose: 1,000 mg**
- **Liquid volume per dose: 10.00 mL**
- **Limit applied: Maximum single dose**
- Nguồn đối chiếu: Python 3.8 decimal: min(80 × 15, 1000) = 1000 mg; 1000 × 1 / 100 = 10 mL

### Edge: daily cap reached

- Weight: 50 kg
- The mg/kg figure is: Per dose
- Dose rate: 20 mg/kg
- Doses per day: 4
- Maximum single dose: 1000 mg
- Maximum per day: 3000 mg
- Liquid strength: amount: 160 mg
- Liquid strength: per volume: 5 mL
- **Weight-based dose before limits: 1,000 mg**
- **Calculated dose: 750 mg**
- **Total per day: 3,000 mg**
- **Liquid volume per dose: 23.44 mL**
- **Limit applied: Maximum daily dose**
- Nguồn đối chiếu: Python 3.8 decimal: min(50 × 20, 1000, 3000 / 4) = 750 mg; 750 × 5 / 160 = 23.4375 mL

### Per-day rate split three ways, no maximums

- Weight: 12 kg
- The mg/kg figure is: Per day, split into doses
- Dose rate: 40 mg/kg
- Doses per day: 3
- Liquid strength: amount: 250 mg
- Liquid strength: per volume: 5 mL
- **Calculated dose: 160 mg**
- **Total per day: 480 mg**
- **Liquid volume per dose: 3.20 mL**
- **Every: 8 h**
- Nguồn đối chiếu: Python 3.8 decimal: 12 × 40 / 3 = 160 mg; 160 × 5 / 250 = 3.2 mL; 24 h / 3 = 28800 s

### BNFC example: 10 kg at 8 mg/kg, max 300 mg

- Weight: 10 kg
- The mg/kg figure is: Per dose
- Dose rate: 8 mg/kg
- Doses per day: 1
- Maximum single dose: 300 mg
- Liquid strength: amount: 160 mg
- Liquid strength: per volume: 5 mL
- **Calculated dose: 80 mg**
- **Limit applied: None**
- Nguồn đối chiếu: BNF for Children, prescribing in children: a 10 kg child should receive 80 mg

### BNFC example: 40 kg at 8 mg/kg, max 300 mg

- Weight: 40 kg
- The mg/kg figure is: Per dose
- Dose rate: 8 mg/kg
- Doses per day: 1
- Maximum single dose: 300 mg
- Liquid strength: amount: 160 mg
- Liquid strength: per volume: 5 mL
- **Calculated dose: 300 mg**
- **Weight-based dose before limits: 320 mg**
- **Limit applied: Maximum single dose**
- Nguồn đối chiếu: BNF for Children, prescribing in children: a 40 kg child should receive 300 mg (rather than 320 mg)

## Câu hỏi

### How do you calculate a dose by weight?

Multiply body weight in kilograms by the dose rate in mg/kg. A 20 kg child at 15 mg/kg gets 20 × 15 = 300 mg per dose. If the rate is per day, divide by the number of doses: 12 kg at 40 mg/kg/day in 3 doses is 480 mg a day, or 160 mg per dose. Convert pounds to kilograms first; 44 lb is 19.96 kg.

### How do you work out how many mL of liquid medicine to give?

Divide the dose in mg by the strength in mg per mL. A 300 mg dose of a 160 mg per 5 mL liquid is 300 × 5 ÷ 160 = 9.375 mL, about 9.4 mL. The FDA's 2011 guidance for over-the-counter liquid medicines asks for a measuring device marked in the same units as the label directions, which is why an oral syringe or the supplied cup is used rather than a kitchen spoon.

### Why is a child's weight-based dose capped?

Because a heavier child's mg/kg dose can exceed the adult dose. The BNF for Children advises that calculated doses should not exceed the adult maximum: at 8 mg/kg with a 300 mg maximum, a 10 kg child receives 80 mg, but a 40 kg child receives 300 mg rather than 320 mg. This calculator applies both a single-dose and a daily maximum and shows which limit, if any, reduced the dose.

### What is the difference between mg/kg per dose and per day?

A per-dose rate gives the amount for each dose; a per-day rate gives the total for 24 hours, which is then divided by the number of doses. At 40 mg/kg, a 12 kg child would get 480 mg per dose on a per-dose reading but 160 mg per dose if the 40 mg/kg is per day in three doses, a threefold difference. Prescriptions state which applies, often as mg/kg/dose or mg/kg/day.

### “Dosage by weight calculator” chính xác đến mức nào?

Độ chính xác phụ thuộc vào dữ liệu nhập và giả định của phương pháp. Phép tính thập phân dùng 50 chữ số có nghĩa, nhưng ước lượng, phương pháp số và dữ liệu nguồn có thể kém chính xác hơn; làm tròn khi hiển thị không loại bỏ các giới hạn đó. Ví dụ có lời giải đã đối chiếu với nguồn độc lập: 7. Ví dụ, “20 kg at 15 mg/kg, 160 mg/5 mL” được kiểm tra bằng Python 3.8 decimal: 20 × 15 = 300 mg; 300 × 5 / 160 = 9.375 mL; 300 × 4 = 1200 mg; 24 h / 4 = 21600 s.

### Phương pháp này lấy từ đâu?

BNF for Children — General guidance, prescribing in children: calculated doses should not exceed the adult maximum (worked example 8 mg/kg, max 300 mg); US FDA — Dosage delivery devices for orally ingested OTC liquid drug products (guidance for industry, 2011).

## Nguồn

- [BNF for Children — General guidance, prescribing in children: calculated doses should not exceed the adult maximum (worked example 8 mg/kg, max 300 mg)](https://bnfc.nice.org.uk/)
- [US FDA — Dosage delivery devices for orally ingested OTC liquid drug products (guidance for industry, 2011)](https://www.fda.gov/regulatory-information/search-fda-guidance-documents/dosage-delivery-devices-orally-ingested-otc-liquid-drug-products)

_Chỉ cung cấp thông tin, không phải tư vấn y tế. Các công thức mô tả quần thể, không đánh giá riêng bạn; hãy trao đổi với nhân viên y tế trước khi hành động theo kết quả._