Tính BMI Miễn Phí Online — Kết Quả Tức Thì

Tính chỉ số BMI online ngay lập tức với công cụ BMI miễn phí của RashTools. Kiểm tra tình trạng chỉ số khối cơ thể (BMI) và khoảng cân nặng lý tưởng ngay trong trình duyệt, không cần đăng ký.

Chiều cao (cm)

Cân nặng (kg)

Thiếu cân

< 18.5

Bình thường

18.5 – 24.9

Thừa cân

25 – 29.9

Béo phì

≥ 30

Calculate BMI in metric or imperial units

Enter height and weight in cm/kg or ft/lb and see your BMI with the standard category it falls into.

Both unit systems, no conversion first

Type 5'9" and 165 lb, or 175 cm and 75 kg. The conversion is handled so you are not doing two calculations.

Try this tool

See where the number sits

The result is shown against the standard ranges, which is more useful than a bare figure with no context.

Open Screen Recorder

A rough screen, not a diagnosis

BMI ignores muscle mass, build and age, so treat it as one signal among several and talk to a professional for anything that matters.

Open File Transfer

Step-by-step guide

How to use BMI Calculator?

Calculate your Body Mass Index in metric or imperial units and see the WHO category.

Step-by-step instructions

1
Choose metric (kg/cm) or imperial (lb/inch) units.
2
Enter your weight and height.
3
See your BMI and the WHO category (underweight, normal, overweight, obese).
4
Use the healthy weight range shown for your height.

Benefits

Works in both metric and imperial units.
Colour-coded category chart.
Also shows the healthy weight range for your height.
Private — nothing is stored.

Who is it for?

Anyone tracking fitness goals
Trainers doing quick client assessments
Health-conscious users checking themselves

Câu hỏi thường gặp

Enter your weight and height into the visible input fields, choose units with the blue "Units" toggle (Metric / Imperial), then press the green "Calculate BMI" button. The tool immediately shows your BMI (kg/m²) to one decimal place, a WHO-based category (Underweight, Normal, Overweight, Obese), and an ideal weight range below the result box. Use the grey "Reset" button to clear fields or the "Copy Result" button to copy the plain-text result (BMI + category) to your clipboard.

The calculator accepts Metric (weight in kg, height in cm) and Imperial (weight in lb, height in ft+in) formats via the "Units" toggle at the top of the form. Metric weight accepts decimals with up to two decimals (e.g., 72.50 kg) and height accepts whole cm or decimals (e.g., 175.3 cm). Imperial accepts pounds (e.g., 160.2 lb) and separate feet/inches fields (5 ft 11 in); the UI converts automatically when you switch units and validates ranges (weight 1–500 kg or 2–1100 lb; height 30–272 cm or 12–107 in).

The calculator uses the standard BMI formula: BMI = weight(kg) / [height(m)]²; when you enter Imperial units it converts lb→kg and ft/in→m before computing. Results are rounded to one decimal place and classification uses WHO cutoffs (Underweight <18.5, Normal 18.5–24.9, Overweight 25.0–29.9, Obesity ≥30.0). This is mathematically accurate for BMI, but BMI itself is a population-level indicator and can misclassify very muscular or elderly people; measurement errors (wrong height or weight) will affect accuracy more than the calculator’s math.

The tool computes an ideal weight range by reversing the BMI formula to give weight values corresponding to WHO's 'normal' BMI range, i.e., BMI 18.5 to 24.9. It displays the minimum and maximum ideal weights in the same units you used (rounded to 0.1 kg or 0.2 lb) and also shows a midpoint weight for BMI 22.0 as a reference. For example, if your height is 175 cm the tool will report ideal weight range ≈ 56.6–76.2 kg and midpoint ≈ 67.3 kg; these are simple BMI-based targets, not personalized clinical recommendations.

Yes — if you enable the optional "Estimate Body Fat" toggle the calculator asks for your age and sex and uses the Deurenberg formula (BodyFat% ≈ 1.20×BMI + 0.23×age − 10.8×sex − 5.4, where sex=1 for males, 0 for females). The tool displays the estimated body fat percentage to one decimal place and notes an expected error margin of about ±3–5% compared with DEXA; it’s intended for quick estimates only. For clinical accuracy use DEXA, hydrostatic weighing, or caliper measurements; the tool does not replace medical tests.

Inputs are validated client-side: weight must be between 1 and 500 kg (2–1100 lb) and height between 30 and 272 cm (12–107 in), age between 5 and 120 years if using the body-fat toggle. The form shows inline red validation messages like "Please enter a valid height between 30 cm and 272 cm" and prevents calculation if required fields are empty or zero to avoid division-by-zero. If you need batch processing for many people, note this single-entry tool does not import CSV — use Excel/Google Sheets or scripts instead.

There’s no built-in file export; use your browser’s Print feature (Ctrl/Cmd+P) to save results as a PDF file (.pdf). Set Page Size to A4 or Letter, margins to "Small" and Background Graphics on if you want the colored header; this produces a clean one-page PDF with the numeric result and notes. For a PNG/JPEG, take a screenshot on desktop (Windows: Win+Shift+S, macOS: Cmd+Shift+4) or mobile; exported PDFs have no watermark and the site does not require signup to generate them.

All calculations run locally in your browser using JavaScript; nothing is uploaded to a server when you press "Calculate BMI." This means your entries never leave your device and no signup is required. The site still loads static assets from the server (HTML/CSS/JS), so ensure you have an internet connection to load the page initially; once loaded you can re-run calculations offline for that session in many browsers.

On iOS Safari the numeric input may display a locale-dependent decimal separator (comma vs period); if you see errors, switch to the system keyboard or enter a dot (.) as the decimal separator. Mobile browsers will open the numeric keypad for weight/height fields but some Android WebViews restrict automatic clipboard access for the "Copy Result" button; use the manual long-press copy in that case. For best experience use Chrome or Firefox on desktop and the latest Safari/Chrome on mobile; older IE and very old Android browsers are not supported and will show a banner asking you to upgrade.

A zero BMI usually means height was left blank or entered as 0 (division-by-zero prevented by validation). Extremely high BMIs often come from unit mix-ups — entering height in cm while the calculator is set to meters or entering inches into the cm field — so double-check the "Units" toggle and use the separate feet/inches fields for Imperial. If you still see an incorrect value, press "Reset" to clear fields and re-enter, ensure you use a dot as the decimal separator if your locale requires it, and verify the inline validation messages.

BMI for children should be interpreted using age- and sex-specific percentiles, which this single-entry adult-focused tool does not compute; the calculator will still compute a raw BMI but won’t return pediatric percentiles. For very muscular athletes and pregnant women, BMI can be misleading because it doesn't distinguish muscle from fat or account for pregnancy-related weight; the tool offers an optional body-fat estimate but that too is approximate. For those groups use pediatric growth charts, sports medicine assessments, or clinical tools (DEXA, professional body composition testing) instead.

This web tool is single-entry only and does not accept CSV or batch uploads; there is no bulk-import button. For batch work use Excel or Google Sheets: the equivalent metric formula is =B2/(C2/100)^2 (weight in B2 in kg, height in C2 in cm); you can copy that down a column and compute WHO categories with nested IFs. The advantage here is instant, annotated single-person results with optional body-fat estimate and a quick PDF/clipboard export, while Excel/Sheets are better for hundreds of rows and automated reporting.

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