[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"$fxLN3MUwXCdr5RPjwZYIDpOj8CHyjOmngWTgoKXPtZbg":3,"$fLJcI1H0dNv7Ti4AHbnyIV20qwLk0TNH2EjvXaPszL_Y":32,"$f3Ft0rKFJHppdzE-vuveecxx1BUcg9iOlMLtyzf_MJDg":47},[4,8,12,16,20,24,28],{"title":5,"slug":6,"path":7},"About Microbeonline.com","about-microbeonline-com","\u002Fabout-microbeonline-com\u002F",{"title":9,"slug":10,"path":11},"About Me","about-me","\u002Fabout-microbeonline-com\u002Fabout-me\u002F",{"title":13,"slug":14,"path":15},"Advertise with Us","advertise-us","\u002Fadvertise-us\u002F",{"title":17,"slug":18,"path":19},"Privacy Policy","privacy-policy","\u002Fprivacy-policy\u002F",{"title":21,"slug":22,"path":23},"Abbreviations","abbreviations","\u002Fabbreviations\u002F",{"title":25,"slug":26,"path":27},"Microbes","microbes","\u002Fmicrobes\u002F",{"title":29,"slug":30,"path":31},"Books","recommended-books","\u002Frecommended-books\u002F",{"type":33,"data":34},"blog",{"slug":35,"title":36,"description":36,"seoTitle":37,"seoDescription":37,"author":38,"createdDate":39,"lastUpdatedDate":40,"draft":41,"category":42,"image":37,"body":43,"faq":44,"tags":45,"related":46},"mcfarland-densitometer-parts-principle-and-operation","McFarland Densitometer: Parts, Principle, and Operation",null,"Ashma Shrestha","2022-11-01","2025-12-29",false,"lab-equipment","Densitometer is laboratory equipment that measures the density or turbidity of photographic objects by measuring the transparency photometrically. The most commonly used densitometer in the microbiology laboratory measures the McFarland standard for antibiotic sensitivity testing.\n\n**The densitometer used in a microbiology laboratory is hence named the McFarland densitometer. It is helpfullaboratory equipmentas an alternative method forpreparing McFarland standardsof bacteria and fungi cell suspension. The McFarland densitometer is calibrated to measure turbidity in the range of 0.3-6.0 McFarland units.**\n\n![DEN-1 Biosan McFarland Densitometers - DEN-1 Biosan McFarland Densitometers](https:\u002F\u002Fassets.microbeonline.com\u002Fblogs\u002FDen-1-biosan-macfarland-densitometer.jpg)Figure: DEN-1 Biosan McFarland Densitometers\n\n## Principle of Densitometer\n\nLike any [spectrophotometer](\u002Fspectrophotometer-principle-parts-types-uses\u002F) and colorimeter, a densitometer also uses the principle of photometry. The light from the stabilized source passes through the optical system inside the densitometers. The light absorption depends on the density of the substances. The absorbance is indirectly proportional to the density, i.e., the denser the substance, the lesser the absorbance. The intensity of light rays transmitted (It) and the intensity of incident ray (Io) is measured to generate optical density. Here, the optical density (OD) or absorbance (A) is the ratio of the intensity of the incident light ray to the intensity of the transmitted light ray {A or OD= -log (It\u002FIo)}. In the case of a McFarland densitometer, the optical density is digitally displayed as McFarland units instead of absorbance.\n\n## Parts of McFarland Densitometer\n\nThe parts of the McFarland densitometer include; **a light source, digital display, tube holder, power switch, and cable for external power supply.**\n\n1. **Light source:** Tungsten light acts as the light source for the densitometer. It is enclosed inside the compact design.\n2. **Digital display:** The readings are displayed digitally in the bright LED (light-emitting diode) display. Here the readings are displayed as McFarland units.\n3. **Tube holder:** It is detachable and can fit 16 mm or 18 mm glass tubes.\n4. **Cable**: It helps to supply electric current for the smooth running of the equipment.\n5. **Power switch:** It is a small switch in the front part near the LED display, and turning it on is the first step for operating the equipment.\n\n![Parts of McFarland Densitmeters - Parts of McFarland Densitometer](https:\u002F\u002Fassets.microbeonline.com\u002Fblogs\u002FParts-of-McFarland-densitometer.png)Figure: Parts of McFarland Densitometer\n\n**Extra Accessories for McFarland densitometer**\n\nThese accessories may or may not be provided with the McFarland densitometer.\n\n1. **Glass tubes:** The McFarland densitometer supports glass tubes of 16 mm and 18 mm in diameter.\n2. **Battery:** Three AA batteries are required to operate DEN-1B by Grant-Bio as a replacement for the electrical supply.\n3. **CKG16 kit:** For calibrating the densitometer that uses 16 mm glass tubes. It consists of 0.5, 1.0, 2.0,3.0, and 4.0 McFarland turbidity standards.\n4. **CKG18 kit:** It is used for the densitometer that uses 18 mm glass tubes. The kit has 0.5, 1.0, 2.0,3.0, and 4.0 McFarland turbidity standards.\n\n## Operating the McFarland Densitometer\n\n### Steps for Operating McFarland Densitometer\n\n1. Connect the cable or place 3 AA inside the battery holder.\n2. Then turn the power switch on.\n3. Firstly place a glass tube without suspension. The reading should be zero.\n4. Pour at least 2ml of the prepared suspension into a glass tube of the preferred diameter.\n5. Place the glass tube in the tube holder.\n6. Once operated, it takes one second to display the McFarland standard. Dilute or mix the suspension as per requirement.\n\n### Calibrating McFarland Densitometer\n\n1. The McFarland standard is provided along with the equipment.\n2. Both 16 mm and 18 mm diameter glass tubes should be used for calibrating.\n3. Firstly place the tube labeled McFarland standard 0.5 into the tube holder. See the reading. If the reading does not show 0.5 McFarland units, shake the glass tube and repeat the step.\n4. Then, simultaneously place the tubes labeled McFarland standard 1.0, 2.0, and 4.0. If the reading, even after proper shaking, shows less or high, the equipment requires maintenance, and contacting authorized companies is suggested.\n\n### Things To Consider\n\n1. Always calibrate the equipment before use.\n2. Perform repair and maintenance from time to time.\n\n**References**\n\n- *Grant SCI UKC – Grosseron*. Densitometers. (n.d.). Retrieved November 1, 2022, from \u003Chttps:\u002F\u002Fwww.grosseron.com\u002FAssets\u002FClient\u002Fimages\u002FGROSSERON\u002FSchema\u002F6234576.pdf>\n- *Den-1, densitometer (suspension turbidity detector) – biosan*. DEN-1, Densitometer (suspension turbidity detector). (n.d.). Retrieved November 1, 2022, from \u003Chttps:\u002F\u002Fbiosan.lv\u002Fmarketplace\u002Fpdf\u002F201\u002F>",[],[],[],[48,55,61,66,70,74,79,84,88,92],{"slug":49,"name":50,"description":51,"image":52,"body":53,"postCount":54},"acharya-tankeshwar","Acharya Tankeshwar","Editor-in-chief","https:\u002F\u002Fassets.microbeonline.com\u002Fauthors\u002Ftankeshwar-acharya-author-microbeonline.jpg","***Tankeshwar Acharya, MSc (Medical Microbiology)***\n\n*Tankeshwar Acharya is an Assistant Professor in the Department of Microbiology at Patan Academy of Health Sciences (PAHS), Nepal, where he has been teaching and practicing clinical microbiology for over 14 years. He is the founder of Microbe Online, one of the leading free microbiology education resources on the web, covering bacteriology, mycology, parasitology, immunology, and clinical laboratory diagnostics written from direct experience in both the classroom and the diagnostic laboratory.*",433,{"slug":56,"name":38,"description":57,"image":58,"body":59,"postCount":60},"ashma-shrestha","SEO Copywriter and Science Communicator\nKathmandu, Nepal","https:\u002F\u002Fassets.microbeonline.com\u002Fauthors\u002Fashma-shrestha.png","Ashma Shrestha holds a Master of Science in Medical Microbiology from the Institute of Science and Technology (IOST), Tribhuvan University, Nepal, where she developed a strong foundation in virology, molecular biology, and diagnostic microbiology.\n\nShe now works as an SEO Copywriter at Resolution Digital, where she combines her scientific training with research-driven content strategy. She is certified in Google Analytics and Google Business Profile (GBP), and brings a data-informed approach to science communication writing content that is not only accurate but structured to reach and serve the students who need it most.\n\nAt microbeonline, Ashma contributes articles primarily in virology and molecular biology, areas she finds most compelling for their mechanistic depth and their growing clinical relevance. Her writing reflects the same standard the site is built on: factual rigor, clear explanation of the *why* behind microbiology concepts, and content that helps students move from memorization to genuine understanding.\n\nShe is passionate about making complex microbiological concepts accessible without sacrificing accuracy; a skill that sits at the intersection of her scientific training and her professional work in content and SEO.",81,{"slug":62,"name":63,"description":64,"image":37,"body":37,"postCount":65},"sushmita-baniya","Sushmita Baniya","Author \u002F Contributor",32,{"slug":67,"name":68,"description":64,"image":37,"body":37,"postCount":69},"samikshya-acharya","Samikshya Acharya",20,{"slug":71,"name":72,"description":64,"image":37,"body":37,"postCount":73},"alisha-tripathi","Alisha Tripathi",6,{"slug":75,"name":76,"description":77,"image":37,"body":37,"postCount":78},"aastha-shrestha","Aastha Shrestha"," Author \u002F Contributor",10,{"slug":80,"name":81,"description":82,"image":37,"body":37,"postCount":83},"guest-author","Guest Author","Guest Author \u002F Contributor",2,{"slug":85,"name":86,"description":64,"image":37,"body":37,"postCount":87},"srijana-khanal","Srijana Khanal",18,{"slug":89,"name":90,"description":82,"image":37,"body":37,"postCount":91},"dr-poonam-acharya","Dr. Poonam Acharya",1,{"slug":93,"name":94,"description":64,"image":37,"body":95,"postCount":96},"nisha-rijal","Nisha Rijal","**Nisha Rijal** is a microbiologist and quality assurance specialist. She served for nearly 12 years as a microbiologist at the National Public Health Laboratory (NPHL), Nepal's national reference laboratory, and continues to work as a consultant microbiologist in international public health organization. ",51]