Scale Explorer

Microscopic

How big is a red blood cell?

Red blood cell · Human

Diameter
7.5–8.7 µm 7.5–8.7 µm range
Thickness
1.7–2.2 µm 1.7–2.2 µm range
Cytosol volume
≈ 0.000000000094 cm³ 0.0000000000032 US fl oz approx.
Diameter (rounded)
≈ 8 µm 8 µm approx.
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Red blood cell, Human hair (width), Grain of sand, Human drawn to the same scaleRed blood cell: diameter 7.5–8.7 µm (too small to see at this scale). Human hair (width): average diameter ≈ 70 µm (too small to see at this scale). Grain of sand: grain diameter (sand size class) 0.0625–2 mm (too small to see at this scale). Human: height 1.61–1.75 m.Red blood cell: 7.5–8.7 µm (too small to see at this scale)Human hair (width): ≈ 70 µm (too small to see at this scale)Grain of sand: 0.0625–2 mm (too small to see at this scale)Human: 1.61–1.75 mHuman1.61–1.75 mRed blood cell7.5–8.7 µm · too small to seeHuman hair (width)≈ 70 µm · too small to seeGrain of sand0.0625–2 mm · too small to see

Red blood cell, Human hair (width) and Grain of sand are too small to see at this scale and are marked with ▲.

Everything is drawn to the same scale, standing on the same ground line. Silhouettes are simplified outlines scaled to the measured dimension. A faded outline shows the top of a size range.

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Dimensions

MeasurementMetricImperialNotesSource
Diameter 7.5–8.7 µm 7.5–8.7 µm Diameter of the normal disc-shaped (discocyte) human red blood cell. Range: varies [1]
Thickness 1.7–2.2 µm 1.7–2.2 µm Thickness of the normal discocyte. Range: varies [1]
Cytosol volume ≈ 0.000000000094 cm³ ≈ 0.0000000000032 US fl oz Volume of the cell's internal fluid, averaging 94 µm³ at 300 mOsmol/kg (1 µm³ = 1e-12 cm³). Approximate [1]
Diameter (rounded) ≈ 8 µm ≈ 8 µm Single rounded value listed by BioNumbers (from Rosen, Optimality Principles in Biology, 1967). Approximate [2]

About the red blood cell

Red blood cells carry oxygen around the body and are the most common cells in human blood. A healthy one is a flexible disc that is thinner in the middle than at the rim, a biconcave shape that lets it squeeze through capillaries narrower than itself. Human red blood cells are about 7.5 to 8.7 µm across and 1.7 to 2.2 µm thick.

  • Red blood cells can deform enough to pass through capillaries narrower than their own resting diameter. [1]

How many fit?

  • ≈ 190,000–230,000 × Red blood cell · diameter lined up end to end match the Human · height
  • ≈ 8.7 × Red blood cell · diameter lined up end to end match the Human hair (width) · average diameter

Counts divide one sourced figure by another. "End to end" uses each object's main measurement; weight and volume rows appear only when both figures are sourced.

How it compares

  • 1/8.7 The width of a human hair is about 8.7 times as wide as a red blood cell is across. See side by side
  • 1/7.2–270 A grain of sand is about 7.2–270 times as wide as a red blood cell is across. See side by side
  • 1/390–670 A black garden ant is about 390–670 times as long as a red blood cell is across. See side by side
  • 1/760–1,000 A grain of rice is about 760–1,000 times as long as a red blood cell is across. See side by side
  • 1/1,100–2,000 A honeybee is about 1,100–2,000 times as long as a red blood cell is across. See side by side
  • 1/190,000–230,000 An average adult is about 190,000–230,000 times as tall as a red blood cell is across. See side by side

Factors compare the diameter of a red blood cell with each object’s own main measurement (height for a human). Where a size varies, the factor is given as a range.

Notes on these figures

  • NCBI Bookshelf (StatPearls) pages returned a CAPTCHA and could not be read, so the dimensions come from a peer-reviewed review hosted on PubMed Central.
  • The 94 µm³ figure is the cytosol (internal fluid) volume, not a separately stated whole-cell volume; converted exactly from µm³.
  • No sourced mass was found.

Sources

  1. MRS Bulletin (via PubMed Central, NIH), Shape and Biomechanical Characteristics of Human Red Blood Cells in Health and Disease (Diez-Silva, Dao, Han, Lim, Suresh, 2010). Accessed 25 September 2026.
  2. BioNumbers, Harvard Medical School, Diameter of red blood cell - BNID 100798. Accessed 25 September 2026.

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