Diagram
Free PNG images in the category “Diagram”: 36 files with transparent background, no sign-up.
Skeletal formulas of fused rings and drug molecules, a small neural network with input and output nodes, a single-line power distribution drawing, a Roman dynasty family tree, a labelled insect cutaway, a pulley lab sheet and a wedge with force arrows.
Subtopics
Filters
Stitch line, Google Translate Website PNG
Stopwatch Sketch, stopwatch, white, hand PNG
Personal computer Frames Line art, Room PNG
Artificial neural network Backpropagation PNG
Wedge Simple machine Angle Force, text PNG
Chemistry Chemical compound Curcumin PNG
Digital camera Drawing Euclidean, hand PNG
Organic acid anhydride Simple aromatic ring PNG
Mercaptopurine Simple aromatic ring PNG
Aromaticity Simple aromatic ring Pyridine PNG
Isoquinoline Naphthalene Aromaticity Simple PNG
Eye, EYE CARE, white, face PNG
Aromaticity Simple aromatic ring PNG
Hepatitis C virus Grazoprevir Chemical PNG
Line Angle White Font, white, text PNG
Quinoline Ether Chemical compound Chemistry PNG
Acridine Chemical structure Simple aromatic PNG
Estrogen receptor Aromaticity Chemical PNG
Stacking Organic chemistry Benzene Pi bond PNG
Pulley Simple machine Laboratory Paper PNG
Possessive Pronoun, Twin Baby, text, hand PNG
The circulatory system of insects Hemolymph PNG
Quad skates Roller skating Ice skating PNG
Chinese ink painting of bamboo wind gossip PNG
Forbidden City Gulou and Zhonglou Ink wash PNG
Principate Julio-Claudian dynasty Family PNG
Sheet Music Piano Sonata No. 14 Song, sheet PNG
Bar chart Graph of a function Line chart PNG
Ring system Planet Computer Icons, planet PNG
Earth Day Natural environment World PNG
God Believe in miracles but trust in Jesus PNG
Agarose Point Angle Roundworm, cherry pull PNG
Rocket Animation Drawing, Space ship PNG
Satellite dish Symbol Satellite truck PNG
Whirlpool Galaxy Nu Earth Drawing Canes PNG
Wedding invitation Business Retail PNG
Not a chart, not an infographic
The Business section keeps numbers in Chart and Graph and finished layouts in Infographic. Diagram is for drawings that explain how something is built or connected: a molecule, a circuit, a lineage, a mechanism. Most of the material is scientific and educational rather than corporate, so expect a lab or a classroom rather than a boardroom.
What makes a usable file
Thin black lines are the whole point, so check the file at full size: bonds and connectors should be continuous, labels readable and not blurred into the strokes. Many diagrams have black lines on a transparent ground, which disappear on a dark slide — put a white panel behind them.
Size and placement
Chemical structures and circuits carry small text, so they need room: half a slide or a full column at least. Shrinking a diagram to thumbnail size leaves a grey tangle. If only part of a structure matters, crop to it instead of scaling everything down.