Punnett Square Calculator

How to use

1. 1Type each parent's genotype in standard notation (Aa, AaBb, AaBbCc, or XAXa style for sex-linked crosses).
2. 2Pick a preset like Monohybrid Aa x Aa or Dihybrid AaBb x AaBb to load a worked example, or use Swap parents to flip them.
3. 3Read the Punnett square grid below; rows are parent 1 gametes, columns are parent 2 gametes, and each cell is a single offspring genotype.
4. 4Check the Genotype ratios and Phenotype ratios panels for the reduced ratio (e.g. 1:2:1 or 9:3:3:1), the count out of the total cells, and the percentage probability.
5. 5Use Copy full report for a plain-text summary or Copy Markdown table to paste the grid into a lab report or worksheet.

About this tool

Punnett Square Calculator builds the offspring grid for any genotype cross and reports the genotype ratio, phenotype ratio, and probability of every outcome. The parser accepts standard Mendelian notation (uppercase letter for the dominant allele, lowercase for the recessive) and supports up to four gene loci in a single cross: monohybrid (Aa x Aa, AA x aa, the textbook test cross Aa x aa), dihybrid (AaBb x AaBb produces the famous 9:3:3:1 phenotype ratio), trihybrid (AaBbCc x AaBbCc, 64 cells, 27:9:9:9:3:3:3:1), and tetrahybrid for advanced problems. Sex-linked inheritance is handled with the XA, Xa, Y notation taught in introductory genetics, so a heterozygous carrier mother crossed with an affected father (XAXa x XaY) splits 1:1:1:1 across carrier daughters, affected daughters, unaffected sons, and affected sons. The implementation enumerates the Cartesian product of per-locus gametes, assembles each offspring genotype with dominant-first allele ordering, classifies the phenotype under complete dominance (A_ at the locus expresses the dominant phenotype, aa expresses the recessive), and tallies the results into clean integer ratios reduced by the greatest common divisor. The grid view color-codes cells by genotype so repeated combinations stand out at a glance, the gamete bar shows what each parent contributes, and the ratio panels report each outcome as a count, a reduced fraction, and a percentage. A Copy Markdown table button exports the grid for lab reports or worksheets, and Copy full report grabs a plain-text summary with the cross, the grid, the genotype ratio table, the phenotype ratio table, and the reduced ratios all in one block. Useful for biology students checking homework, AP and IB Biology revision, teachers preparing genetics handouts, tutors walking through Mendelian inheritance step by step, premed students reviewing genetics for the MCAT, and anyone who needs a quick cross result without drawing the grid by hand. The model assumes Mendelian inheritance: independent assortment of unlinked loci, equal gamete proportions, and complete dominance. Linkage, recombination frequencies, polygenic traits, incomplete dominance, and codominance with multiple alleles are out of scope for a single Punnett square; treat each highlight as the textbook result, not a clinical prediction. Everything runs locally in your browser. No genotype, trait name, or result is uploaded.

Free to use. Works in your browser. No signup, no login.