I was just studying this yesterday! In a nutshell, RBC's are about 7-8 microns in diameter, whilst WBC's are around 10-14 microns. here's my notes from my class's experiment:
AIM To estimate the size of RBCs and WBCs
RISK ANALYSIS / SAFETY PRECAUTIONS
Broken slides may cause cuts - put in bin with dustpan & brush, avoid touching broken glass. Using a fresh blood sample poses a risk of contracting any blood borne diseases eg HIV, hepatitis. Use a commercial blood slide / prepared blood slide.
EQUIPMENT
Commercial blood slide, light microscope, minigrid, pencil, ruler, calculator.
METHOD
• Set up microscope
• Focus on 0.1mm² minigrid at 400x magnification. Count number of squares across diameter, thus estimating field of view. eg if 4 squares can fit across, then field of view is approximately 0.4mm or 400µm wide (1000µm = 1mm)
• Remove minigrid & replace with commercial blood slide. Using 400x magnification, count/estimate the number of RBCs across field of view. Eg 50RBCs fit across field of view
• Divide field of view by number of RBCs (400µm / 50) therefore each blood cell is approximately 8µm in diameter.
• WBCs are roughly 1.5x larger than RBCs. Therefore WBCs are approximately 12µm in diameter.
Hope that helps.
Ali