4.5 — Find surface areas (including formulae and net method).
4.5 — Use Pythagoras to find dimensions in 3D.
Prisms (including cuboids and cylinders)
V= cross-section area × length. Uniform along length.
Prism = uniform cross-section.
General formula: V= area of cross-section ×l.
Specific:
Shape
Volume
Cube
s3
Cuboid
lwh
Triangular prism
21bh△×l
Cylinder
πr2h
Surface area of cylinder: 2 circles + curved (rectangle when unrolled).
SAcylinder=2πr2+2πrh.
The curved surface unrolls to a rectangle: width = circumference 2πr, height = h.
Worked qualitative. Why is the curved surface of a cylinder a rectangle?
Imagine cutting and unrolling.
Width: circumference 2πr.
Height: h.
Area: 2πr×h=2πrh.
Edexcel tip. Always state UNITS for volume (cm³, m³). Mark schemes deduct for using cm².
V= cross-section × length.
Cuboid: lwh.
Cylinder: πr2h.
Cylinder SA: 2πr2+2πrh.
Pyramids and cones
V=31× base × height. Cone curved surface uses slant.
Pyramid volume: V=31× base area ×h.
The 31 is universal for pyramids/cones — exactly 31 of the bounding prism/cylinder.
Cone-specific:
Vcone=31πr2h
SAcone=πr2+πrl
where h = perpendicular height, l = SLANT height.
h,r,l form a right triangle:h2+r2=l2 (Pythagoras).
Perpendicular height h, radius r and slant height l form a right triangle.
Worked example. Cone with r=5, l=13.
Find h: h2=169−25=144, h=12.
V=31π×25×12=100π.
Curved surface: π×5×13=65π.
Total SA: 25π+65π=90π.
Worked qualitative. Why is cone volume 31 of cylinder volume (same r,h)?
Cylinder: πr2h.
Cone fits inside it.
Calculus shows the cone is exactly 31.
Geometrically: cones with the same base and apex tapered uniformly.
Edexcel tip. Pyramids/cones use PERPENDICULAR height for VOLUME, SLANT height for CURVED SURFACE. Don't confuse.
V=31× base × height.
Cone: 31πr2h.
Curved surface: πrl.
Use Pythagoras for h,r,l.
Spheres
V=34πr3, SA=4πr2.
Sphere formulas:
V=34πr3SA=4πr2
Both use the radius r.
A hemisphere is exactly half a sphere; its surface adds a flat circular base.
Hemisphere (half a sphere):
Vhemi=32πr3.
SAhemi=2πr2 (curved) plus πr2 (circular base) = 3πr2.
Worked example. Sphere with r=6.
Volume: 34π×216=288π cm³.
Surface: 4π×36=144π cm².
Worked qualitative. Why is sphere SA 4πr2, exactly 4× area of equator circle?
Beautiful result from calculus.
Beyond IGCSE proof — but memorise.
Edexcel tip. When the question says 'in terms of π', leave answer as 288π, not the decimal.
V=34πr3.
SA=4πr2.
Hemisphere: half + circular base.
Both use r.
3D Pythagoras
Used for finding diagonals of cuboids and other 3D distances.
3D Pythagoras for the long diagonal of a cuboid:
If a cuboid has sides a,b,c, the long diagonal d satisfies:
d2=a2+b2+c2
Why? First, the floor diagonal: dfloor2=a2+b2 (2D Pythagoras).
Then, considering the long diagonal as the hypotenuse of a right triangle with sides dfloor and c (height):
d2=dfloor2+c2=a2+b2+c2.
Pythagoras twice: first the floor diagonal, then combine with height c.
Worked example. Cuboid 3×4×12. Long diagonal?
d2=9+16+144=169.
d=13.
Worked qualitative. What's the diagonal of a unit cube (1×1×1)?
d2=1+1+1=3.
d=3≈1.732.
Edexcel tip. 3D Pythagoras applies wherever you can find a right triangle in 3D. Often combined with cones or other shapes.
d2=a2+b2+c2 for cuboid diagonal.
Apply 2D Pythagoras twice.
Find right triangles within the 3D shape.
Common in cone problems too (h,r,l).
How it’s examined
3D shapes appear every Higher Tier paper (5-8 marks). Often combined with Pythagoras or scale factors. Examiner reports flag (1) using slant for volume, (2) forgetting 31 for pyramids/cones, (3) wrong units (cm² vs cm³).
Worked examples, formulae, definitions and the mistakes examiners flag — everything you need to push from a pass to an A*.
Take this whole topic with you
Download a branded revision sheet — worked examples, formulae, definitions and common mistakes for 3D Shapes and Volume, ready to print or save as PDF.
Step-by-step worked examples — 3D Shapes and Volume
Step-by-step solutions to past-paper-style questions on 3d shapes and volume, written exactly the way a tutor would explain them at the board.
1Volume of a cuboid
Foundation• cuboid
▼
Question
Cuboid: 5×3×4 cm. Volume?
Step-by-step solution
Step 1
V=length×width×height.
Step 2
V=5×3×4=60 cm³.
Answer
60 cm³
2Cylinder volume and surface area
Higher• Adapted from 4MA1/1H May/Jun 2024 Q13• cylinder
▼
Question
Cylinder: radius 4 cm, height 10 cm. Find (a) volume, (b) total surface area in terms of π.
(c) Surface: base circle πr2=25π. Curved: πrl=5×13×π=65π.
Step 4
Total: 25π+65π=90π cm².
Answer
(a) h=12 cm (b) V=100π (c) SA =90π cm²
Examiner tip
Cone volume uses PERPENDICULAR height. Curved surface uses SLANT height. Edexcel mark schemes are precise about this.
4Sphere
Higher• Adapted from 4MA1/2H Jan 2024 Q14• sphere
▼
Question
Sphere of radius 6 cm. Find (a) volume, (b) surface area. In terms of π.
Step-by-step solution
Step 1
(a) V=34πr3=34π×216=288π cm³.
Step 2
(b) SA=4πr2=4π×36=144π cm².
Answer
(a) V=288π (b) SA =144π cm²
5Prism volume
Foundation• prism
▼
Question
Triangular prism: triangle base 6 cm × height 4 cm; prism length 10 cm. Volume?
Step-by-step solution
Step 1
Cross-sectional area (triangle): 21×6×4=12 cm².
Step 2
Volume = cross-section × length: 12×10=120 cm³.
Answer
120 cm³
Key Formulae — 3D Shapes and Volume
The formulae you need to memorise for 3d shapes and volume on the Pearson Edexcel IGCSE 4MA1 paper, with every variable defined in plain English and a note on when to use it.
Cuboid volume
V=lwh
l,w,h
length, width, height
When to use
Cuboids and cubes.
Example
5×3×4=60.
Prism volume
V=Across-section×l
Across-section
area of the cross-section
l
length of prism
When to use
Any prism (uniform cross-section). Includes cuboids.
Example
Triangle base area 12, length 10: V=120.
Cylinder
V=πr2h,SA=2πr2+2πrh
r
radius
h
height
When to use
Cylinders. SA = 2 circles + curved surface.
Example
r=4,h=10: V=160π, SA=112π.
Pyramid volume
V=31×base area×h
h
perpendicular height
When to use
Pyramids (square, triangular, any base).
Example
Square base area 16, height 9: V=31×16×9=48.
Cone
V=31πr2h,SA=πr2+πrl
r
radius
h
perpendicular height
l
slant height
When to use
Cones. Curved surface uses SLANT height.
Example
r=5,h=12: V=100π. l=13: SAcurve=65π.
Sphere
V=34πr3,SA=4πr2
r
radius
When to use
Spheres.
Example
r=6: V=288π, SA=144π.
Key Definitions and Keywords — 3D Shapes and Volume
Definitions to memorise and the exact keywords mark schemes credit for 3d shapes and volume answers — sharpened from recent examiner reports for the 2026 Pearson Edexcel IGCSE 4MA1 sitting.
Prism
Examiner keyword
A 3D shape with a UNIFORM cross-section throughout its length.
A 3D shape with a polygon base, sides meeting at a single apex.
Slant height vs perpendicular height (cone/pyramid)
Slant: along the surface. Perpendicular: 90° from base to apex. Related by Pythagoras.
Common Mistakes and Misconceptions — 3D Shapes and Volume
The traps other students keep falling into on 3d shapes and volume questions — taken from recent Pearson Edexcel IGCSE 4MA1 examiner reports and mark schemes — and how to avoid them.
✕Using slant instead of perpendicular height for volume